Ceramics in the solid solution system, (1 − x)Ba_0.8Ca_0.2TiO₃–xBi(Mg_0.5Ti_0.5)O₃, were prepared by a conventional mixed oxide route. Single-phase perovskite-type X-ray diffraction patterns were observed for compositions x < 0.6. A change from tetragonal to single-phase cubic X-ray patterns occurred at x ≥ 0.1. Dielectric measurements indicated relaxor behavior for x ≥ 0.1. Increasing the Bi(Mg_0.5Ti_0.5)O₃ content improved the temperature sensitivity of relative permittivity ϵ_r at high temperatures. At x = 0.5, a near-plateau relative permittivity, 835 ± 40, extended across the temperature range, 65°C–550°C; the permittivity increased at x = 0.6 to 2170 ± 100 for temperatures 160°C–400°C (1 kHz). The corresponding loss tangent, tanδ, was ≤0.025 for temperatures between 100°C and 430°C for composition x = 0.5; at x = 0.6, losses increased sharply at >300°C. Comparisons of dielectric properties with other materials proposed for high-temperature capacitor applications suggest that (1 − x)Ba_0.8Ca_0.2TiO₃–xBi(Mg_0.5Ti_0.5)O₃ ceramics are a promising base material for further development.

CaTiO₃ perovskite has been proposed as a ceramic waste form for immobilization of ⁹⁰Sr. Nonradioactive coprecipitated xerogel powders with nominal atomic ratios of Ca:Zr:Ti = 0.75:0.25:1.00 were synthesized to mimic the fate of (Ca_0.75⁹⁰Sr_0.25)TiO₃ solid solution after complete decay of the Sr and its intermediate product Y to stable Zr when an excess B⁴⁺ (Ti and ⁹⁰Zr) cations will present. Ca:Ti = 1.00:1.00 samples were used as a reference. The powders were heated to various conditions to explore the thermodynamic stability of its oxides. The heated Ca:Zr:Ti = 0.75:0.25:1.00 samples formed a major orthorhombic Ca(Zr_1−xTi_x)O₃ perovskite phase. The Ti/(Ti + Zr) ratio of the perovskite preserves its nominal ratio at 600°C. The Zr rejects from the Ca(Zr_1−xTi_x)O₃ with further increasing the temperature, following the formation of Ca–Ti–Zr–O secondary phases. This study indicates a tendency of the Zr to segregate from an original (Ca,Sr)TiO₃ waste form when the stoichiometry is controlled by the conversion of Sr to Zr (in normal oxidation states).

The production of Athenian fine ware pottery, produced between the 6th and 4th centuries B.C., required alternating the high-temperature kiln between oxidative and reductive environments during a single firing to create the iconic red and black decorative scenes. Here, we show that the production of this pottery was even more complex, with vessels subjected to two, or possibly more, firings in the kiln, with applications of slip between each firing. On a representative sherd, we compared three painted black decorative features—relief line, contour line, and background slip. Scanning transmission electron microscopy (STEM) of the slips revealed that the relief line had a more melted microstructure than either the contour line or background slip. By characterizing the chemistry and micromorphology of the slips, we find that the relief line microstructure could only be produced through a separate firing, at a hotter temperature, than the other two decorative features.

Phase stability, elastic behavior, and pressure-induced structural evolution of synthetic boron-mullite Al₅BO₉ (a = 5.6780(7), b = 15.035(6), and c =7.698(3) Å, space group Cmc2₁, Z = 4) were investigated up to 25.6(1) GPa by in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell (DAC) under hydrostatic conditions. No evidence of phase transition was observed up to 21.7(1) GPa. At 25.6(1) GPa, the refined unit-cell parameters deviated significantly from the compressional trend, and the diffraction peaks appeared broader than at lower pressure. At 26.7(1) GPa, the diffraction pattern was not indexable, suggesting amorphization of the material or a phase transition to a high-pressure polymorph. Fitting the P–V data up to 21.7(1) GPa with a second-order Birch–Murnaghan Equation-of-State, we obtained a bulk modulus K_T0 = 164(1) GPa. The axial compressibilities, here described as linearized bulk moduli, are as follows: K_T0(a) = 244(9), K_T0(b) = 120(4), and K_T0(c) = 166(11) GPa (K_T0(a):K_T0(b):K_T0(c) = 2.03:1:1.38). The structure refinements allowed a description of the main deformation mechanisms in response to the applied pressure. The stiffer crystallographic direction appears to be controlled by the infinite chains of edge-sharing octahedra running along [100], making the structure less compressible along the a-axis than along the b- and c-axis.

Highly c-axis-oriented Ca₃Co_4−xCu_xO_9+δ (x = 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO₃ (001) single-crystal substrates. X-ray diffraction, field-emission scanning electronic microscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ with quadruplicated rock-salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu-doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu-doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu-doped Ca₃Co₄O_9+δ thin films could be a promising candidate for thermoelectric applications.

Theoretical analyses of shrinkage and distortion kinetics during sintering of bilayered porous structures are carried out. The developed modeling framework is based on the continuum theory of sintering; it enables the direct assessment of the cofiring process outcomes and of the impact of process controlling parameters. The derived “master sintering curve”-type solutions are capable of describing and optimizing the generic sintering shrinkage and distortion kinetics for various material systems. The approach utilizes the material-specific parameters, which define the relative kinetics of layer shrinkages such as the relative intensity of sintering, and employs the conversion between real and specific times of sintering. A novel methodology is also developed for the determination of the ratio of the shear viscosities of the layer's fully dense materials. This new technique enables the determination of all input parameters necessary for modeling sintering of bilayers using experimental techniques similar to optical dilatometry applied to each individual layer and to a symmetric trilayered porous structure based on the two-layer materials utilized in the bilayered system. Examples of sintering different porous bilayered systems are presented to justify the capability of the model in predicting and optimizing sintering kinetics.

A mixture of ultrafine submicrometer-sized BaCO₃ powder and TiO₂ (rutile) powder was calcined in air at 700°C, 800°C, and 900°C, and then quenched to liquid nitrogen temperature in each case. The cross-sectional quenched specimens were characterized by spatially resolved electron energy-loss spectroscopy (SR-EELS). The energy-loss near-edge structures (ELNES) were sequentially extracted at 1.3 to 5.3 nm in width from SR-EELS image obtained from the rectangularly cut SR-EELS slit aperture put on the synthesized BaTiO₃ layer and TiO₂ rutile powder. The ELNES of Ti-L_2,3 edges and Ba-M_4,5 edges clearly show fine structure changes from the surface of BaTiO₃ layer to the TiO₂ bulk region reflected from crystallinity of synthesized BaTiO₃, lattice distortion of TiO₂ caused by Ba diffusion, and lattice misfit between BaTiO₃ and TiO₂ without formation of Ba₂TiO₄ and other titanate phases.

Searching for an efficient non rare earth-based oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm and unexcitable by green light, is essential for the development of warm white light emitting diodes (WLEDs). Here, we report a promising and orderly-layered candidate: Sr₄Al₁₄O₂₅:Mn⁴⁺ with CIE color coordinates (0.722, 0.278). It has higher luminescence efficiency particularly upon blue excitation and is much cheaper than the commercial red phosphor 3.5MgO·0.5MgF₂·GeO₂:Mn⁴⁺ (MMG:Mn⁴⁺). In sharp contrast to Eu²⁺-doped (oxy)nitrides, the phosphor can be synthesized by a standard solid-state reaction at 1200°C in air. The effects of flux boron content, environment, and preparation temperature, sintering dwelling time as well as Mn concentration have been systematically investigated for establishing the optimal synthesis conditions. The low temperature emission spectra reveal that there are at least three types of Mn⁴⁺ ions in Sr₄Al₁₄O₂₅:Mn⁴⁺ due to the substitution for the distorted octahedral Al³⁺ sites. The AlO₆ layers where Mn⁴⁺ prefers to reside are well separated from one another by AlO₄ tetrahedra in one dimension parallel to axis a. This scenario can efficiently isolate Mn⁴⁺ ions from local perturbations, thereby enabling the high efficiency of luminescence. The energy transfer rates and mechanism are discussed.

Copper and iron in glasses constitute classical aims of study because of the optical effects that they produce. Structured materials are also interesting due to the incorporated functionalities derived from their spatial organization. Here, CuO and Fe₂O₃ were incorporated into a standard glass, from which glass coatings with different thicknesses were studied. Whereas iron cations dissolved in the glassy matrix, copper cations saturated it and crystallized at the surface, forming a hierarchical microstructure. The surface microstructure consisted of crystallizations of Tenorite (CuO) forming interconnected walls. The walls surrounding areas of glassy matrix gave rise to a cells microstructure. Rutherford Backscattering Spectrometry provided the composition of the samples with high depth resolution, and Raman Confocal Microscopy determined the phases location and their distribution forming the microstructure. The joint information from both techniques allowed high chemical and spatial resolution of the main cations location for the hierarchical surface microstructure.

Crystal structure and cation distribution of nanocrystalline SrFe_1−xTi_xO_3−δ (0 ≤ x ≤ 0.3) synthesized by combined high-energy ball milling and solid-state reactions are investigated using Neutron powder diffraction and Mössbauer spectroscopy. Ti doping stabilizes the single phase tetragonal structure with I4/mmm space group up to x = 0.3. The neutron and Mössbauer data confirm that Fe exists in three different sites both crystallographically as well as magnetically in all the four compositions. The cation distribution at various sites is established through Rietveld refinement.

Fatigue failure is a concern when high-strength, high-toughness silicon nitride ceramics are used in mechanical components and the growth of natural flaws will determine the usable upper bound strength. In this study a fracture resistance curve (R-curve) model is incorporated into an established method for deducing natural flaw growth rates from a combination of strength and fatigue life data for smooth specimens. Experimental data for a commercial silicon nitride, SL200, were examined. When compared with results deduced using a constant fracture toughness model, the new method gives more physically realistic growth rate results. Specifically, by incorporating the R-curve the deduced fatigue threshold is equal to the reported intrinsic toughness for crack propagation of 2.2 MPa√m, whereas the constant fracture toughness model gives a physically unrealistic threshold value. Furthermore, much better agreement is achieved with the growth rates measured using macroscopic compact-tension specimens. Overall, it is concluded that the R-curve effect should not be ignored when deducing the fatigue crack growth rates of natural flaws in high-toughness silicon nitride ceramics.

Although HA is highly biocompatible, one of the major disadvantages of HA include the lack of antibacterial property. In an earlier study, we demonstrated the potential role of magnetic field stimulation on bactericidal property in vitro. Following this, it was hypothesized that antibacterial property can be realized if bacteria are grown on magnetic biocomposites in vitro. In addressing this issue, this study demonstrates the development of HA-Fe₃O₄-based magnetic substrate with multifunctional properties. For this purpose, HA-xFe₃O₄ (x: 10, 20 and 40 wt%) powder compositions were sintered using uniquely designed spark plasma sintering conditions (three stage sintering with final holding temperature of 1050°C for 5 min). A saturation magnetization of 24 emu/g is measured with HA-40%Fe₃O₄. Importantly, all the HA-Fe₃O₄ composites demonstrated bactericidal property by rupturing the membrane of Escherichia coli bacteria, while supporting cell growth of metabolically active human fetal osteoblast cells over 8 d culture. A systematic decrease in bacterial viability with Fe₃O₄ addition is consistent with a commensurate increase in reactive oxygen species (ROS).

Colloidal processing of the Ultra-High Temperature Ceramic (UHTC) zirconium diboride (ZrB₂) to develop near−net-shaping techniques has been investigated. The use of the colloidal processing technique produces higher particle packing that ultimately enables achieving greater densification at lower temperatures and pressures, even pressureless sintering. ZrB₂ suspension formulations have been optimized in terms of rheological behavior. Suspensions were shaped into green bodies (63% relative density) using slip casting. The densification was carried out at 1900°C, 2000°C, and 2100°C, using both hot pressing at 40 MPa and pressureless sintering. The colloidally processed materials were compared with materials prepared by a conventional dry processing route (cold pressed at 50 MPa) and subjected to the same densification procedures. Sintered densities for samples produced by the colloidal route are higher than produced by the dry route (up to 99.5% relative density by hot pressing), even when pressureless sintering is performed (more than 90% relative density). The promising results are considered as a starting point for the fabrication of complex-shaped components that can be densified at lower sintering temperatures without pressure.

The intrinsic mechanical properties of 20 MAX-phase compounds are calculated using an ab initio method based on density functional theory. A stress versus strain approach is used to obtain the elastic coefficients and thereby obtain the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio based on the Voigt–Reuss–Hill (VRH) approximation for polycrystals. The results are in good agreement with available experimental data. It is shown that there is an inverse correlation between Poisson's ratio and the Pugh ratio of shear modulus to bulk modulus in MAX phases. Our calculations also indicate that two MAX compounds, Ti₂AsC and Ti₂PC, show much higher ductility than the other compounds. It is concluded that the MAX-phase compounds have a wide range of mechanical properties ranging from very ductile to brittle with the “A” in the MAX phase being the most important controlling element. The measured Vickers hardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations.

The preparation of platelike NaNbO₃ grains via single-step molten salt synthesis using Bi₂O₃, Na₂CO₃, Nb₂O₅, and NaCl as reactants was examined. When a new alumina crucible was used, platelike NaNbO₃ grains were obtained, but a repeatedly used alumina crucible resulted in irregularly shaped NaNbO₃ grains. When a platinum crucible was used, even NaNbO₃ could not be obtained. Addition of alumina substrates and alumina granules to the reaction mixture in the platinum crucible resulted in the formation of platelike NaNbO₃ grains and second-phase grains. The second-phase grains, which were composed of Al₂O₃, Bi₂O₃, Na₂O, and Nb₂O₅ and had a pyrochlore structure, could be removed by sieving. The second phase acted as a scavenger for Bi₂O₃ and hence, the possibility of using another scavenger was attempted. The new scavenger was a mixture of Na₂CO₃ and Nb₂O₅, and using them, platelike NaNbO₃ grains were successfully obtained with NaNb₅Bi₂O₁₆ as a byproduct, which could then be removed by sieving.

Transparent glass-ceramics containing Li₂ZnSiO₄:Fe nanocrystals were prepared by melt-quenching method followed by post-heat-treatment process. The as-prepared glasses and glass-ceramics showed red to near-infrared photoluminescence centered at 730 nm, ascribed to Fe³⁺ ions in tetrahedral coordination. The intensity of the photoluminescence was enhanced by two technologically simple techniques—the valence state of irons was controlled from Fe²⁺ to Fe³⁺ ions using oxidizing agents, whereas the coordination state was compulsorily converted from octahedral to tetrahedral symmetry by performing a ceramization process. The presence of Fe²⁺ ions was considered a major origin for Fe³⁺ photoluminescence quenching. Oxidation of Fe²⁺ and conversion of Fe²⁺ ions into tetrahedral symmetry contribute to suppression of energy transfer from Fe³⁺ emitters to Fe²⁺ quenching centers.

(1−x)Pb(Hf_1−yTi_y)O₃–xPb(Yb_0.5Nb_0.5)O₃ (x = 0.10–0.44, y = 0.55–0.80) ceramics were fabricated. The morphotropic phase boundary (MPB) of the ternary system was determined by X-ray powder diffraction. The optimum dielectric and piezoelectric properties were achieved in 0.8Pb(Hf_0.4Ti_0.6)O₃–0.2Pb(Yb_0.5Nb_0.5)O₃ ceramics with MPB composition, where the dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p, and Curie temperature T_c were found to be on the order of 1930,480 pC/N, 62%, and 360°C, respectively. The unipolar strain behavior was evaluated as a function of applied electric field up to 50 kV/cm to investigate the strain nonlinearity and domain wall motion under large drive field, where the high field piezoelectric d₃₃* was found to be 620 pm/V for 0.82Pb(Hf_0.4Ti_0.6)O₃–0.18Pb(Yb_0.5Nb_0.5)O₃. In addition, Rayleigh analysis was carried out to study the extrinsic contribution, where the value was found to be in the range 2%–18%.

The edge chipping test was used to measure the fracture resistance of alumina/alumina-zirconia laminated structures. Tailored, symmetrical laminated structures were prepared with a variety of layer thickness. The laminates had a significantly greater edge chipping resistance. Laminates with thin layers were just as effective in impeding edge chips as laminates with thick layers.

Diagram of the phase transformation behavior of GeS₂–Ga₂S₃–CsI glasses is realized in this article and the structure-property dependence of the chalcogenide glasses is elucidated using differential scanning calorimetry and Raman spectroscopy. We observe the compositional threshold of crystallization behavior locates at x = 6–7 mol% in (100−x)(0.8GeS₂–0.2Ga₂S₃)–xCsI glasses, which is confirmed by the thermodynamic studies. Structural motifs are derived from the Raman result that [Ge(Ga)S₄], [S₂GeI₂], [S₃GaI], and [S₃Ga–GaS₃] were identified to exist in this glass network. Combined with the information of structural threshold, local arrangement of these structural motifs is proposed to explain all the experimental observations, which provides a new way to understand the correlation between crystallization behavior and network structure in chalcogenide glasses.

Silicon Carbide whiskers have been synthesized using silica sol and activated carbon as reagents via microwave heating without the presence of any of the catalysts, such as Fe, Ni, and Al etc.. The synthesized whiskers were separated and concentrated from the as-synthesized products using the gravity concentration process. The dielectric properties of the concentrated SiC whiskers were investigated in the frequency range 2–18 GHz. The results indicate that the SiC whiskers exhibit higher dielectric permittivity and loss tangent than those of SiC powders, respectively, due to the high density of stacking faults formed in the SiC whiskers prepared by microwave heating.

This study reports on the fabrication and characterization of polymer-derived amorphous and nano-grained SiC, by controlled pyrolysis of allylhydridopolycarbosilane (AHPCS) under inert atmosphere. Processing temperatures and hold times at final temperatures are varied to study the influence of processing parameters on the structure and resulting properties. Chemical changes, phase transformations, and microstructural changes occurring during the pyrolysis process are studied. Polymer cross-linking and polymer to ceramic conversion is studied using infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are performed to monitor the mass loss and phase change as a function of temperature. X-ray diffraction studies are performed to study the intermediate phases and microstructural changes. Hardness and modulus measurements are carried out using instrumented nanoindentation to establish processing-property-structure relationship for SiC derived from the polymer precursor. It is seen that the presence of nanocrystalline domains in amorphous SiC significantly influences the modulus and hardness. A nonlinear relationship is observed in these properties with optimal mechanical properties observed for SiC processed to 1150°C for 1 h hold duration, having average grain size of 3 nm. In addition, bulk mechanical characterization, in terms of biaxial flexure strength, is done for SiC–SiC particulate composites purely derived from the polymer precursor.

The transformation process of clay minerals into pozzolanic products for use as active additives in cement matrixes has been closely studied by both the scientific community and the cement industry. Sourcing these additions from recycled waste products is widely prioritized in environmental policies, because of their associated environmental benefits. This article reports an exhaustive analysis of slate waste in Spain, for its eventual use as an alternative source of pozzolans, based on activated phyllosilicates. The analysis examines the effect of activation conditions on mineralogy and the formation and evolution of the hydrated phases that form during the pozzolanic reaction at 28 days. The results show good pozzolanic activity in the starting slate wastes activated between 800°C and 1100°C of temperature for 2 h of retention, on which basis 1000°C and 2 h were recommended as the more suitable activation conditions for these activated slate wastes (ASW), as total destruction of all phyllosilicates is ensured under those conditions. The hydrated phases formed during the pozzolanic reaction in the ASW/Ca(\OH)₂ system were calcium silicate hydrate gels (CSH), randomly interstratified chlorite (Cl) /smectite with variables containing chlorite/smectite ratios 30% chlorite, 40% chlorite, 50% chlorite, 60% chlorite, respectively, and monosulfoaluminate (C₃A·SO₄Ca·12H₂O) directly related to the activation process used in this article. All of these findings support the viability of slate waste for use as a pozzolanic addition.

The reaction behavior of α-Boron nitride (BN) powder in wet air was investigated at 1273 K using thermogravimetric (TG) analysis, X-ray diffraction (XRD), and mass spectrometry. Scanning electron microscopy and electron probe X-ray microanalysis (EPMA) were used to analyze the morphological and elemental development of the sample. The results show that the reaction process consists of two stages: the oxidation of BN powder to form B₂O₃ and the further reaction of B₂O₃ with H₂O. In the first stage, the oxidation reaction occurs very quickly and can be described by Chou's model. In the second stage, the reaction rate followed the linear rate law.

Experimental analyses of shrinkage and distortion kinetics during sintering of bilayered porous and dense gadolinium-doped ceria Ce_0.9Gd_0.1O_1.95−δ structures are carried out, and compared with the theoretical models developed in Part I of this work. A novel approach is developed for the determination of the shear viscosities ratio of the layer fully dense materials. This original technique enables the derivation of all the input parameters for the bilayer sintering modeling from one set of optical dilatometry measurements, including the conversion between real and specific times of sintering, the layers’ relative sintering intensity, and the shear viscosities ratio of the layer fully dense materials. These optical dilatometry measurements are conducted simultaneously for each individual layer and for a symmetric trilayered porous structure based on the two layers utilized in the bilayered system. The obtained modeling predictions indicate satisfactory agreement with the results of sintering of a bilayered cerium–gadolinium oxide system in terms of distortion and shrinkage kinetics.

We study ionic conductivity of heavily doped ceria, doping level close to 50 mol% with multiple lanthanides in the temperature range of 200°C–500°C. The doped ceria is found to be single fluorite phase, where unit cell is dilated to 0.5527 nm, compared with pure ceria (0.5422 nm). Electrical characterization by impedance spectroscopy reveals that sample sintered at lower temperature (1400°C) has consistently higher bulk conductivity compared to sample sintered at higher (1600°C) temperature, throughout the temperature range studied. Activation energy for oxygen vacancy diffusion is close to 1 eV, indicating lesser association of defects with the dopants compared with other heavily doped ceria reported in literature (activation energy ~1.4 eV). The best ionic conductivity is found to be 1.58 × 10⁻³ S/cm at 500°C, which is much higher compared with heavily doped ceria reported in literature.

In this article, perovskite-structured BiFeO₃–Bi(Zn_1/2Ti_1/2)O₃–PbTiO₃ (BF–BZT–PT) ternary solid solutions were prepared with traditional solid-state reaction method and demonstrated to exhibit a coexistent phase boundary (CPB) with Curie temperature of T_C~700°C in the form of ceramics with microstructure grain size of several micron. It was found that those CPB ceramics fabricated with conventional electroceramic processing are mechanically and electrically robust and can be poled to set a high piezoelectricity for the ceramics prepared with multiple calcinations and sintering temperature around 750°C. A high piezoelectric property of T_C = 560°C, d₃₃ = 30 pC/N, ε₃₃^T/ε₀ = 302, and tanδ = 0.02 was obtained here for the CPB 0.53BF–0.15BZT–0.32PT ceramics with average grain size of about 0.3 μm. Primary experimental investigations found that the enhanced piezoelectric response and reduced ferroelectric Curie temperature are closely associated with the small grain size of microstructure feature, which induces lattice structural changes of increased amount ratio of rhombohedral-to-tetragonal phase accompanying with decreased tetragonality in the CPB ceramics. Taking advantage of structural phase boundary feature like the Pb(Zr,Ti)O₃ systems, through adjusting composition and microstructure grain size, the CPB BF–BZT–PT ceramics is a potential candidate to exhibit better piezoelectric properties than the commercial K-15 Aurivillius-type bismuth titanate ceramics. Our essay is anticipated to excite new designs of high–temperature, high–performance, perovskite-structured, ferroelectric piezoceramics and extend their application fields of piezoelectric transducers.

We report nanocomposites of increased dielectric permittivity, enhanced electric breakdown strength and high-energy density based on surface-modified BaTiO₃ (BT) nanoparticles filled poly(vinylidene fluoride) polymer. Polyvinylprrolidone (PVP) is used as the surface modification agent and homogeneous nanocomposite films have been prepared by solution casting processing. The dielectric permittivity of the nanocomposite with treated BT is higher than those with untreated BT and reaches the maximum value of 77 (1 kHz) at BT concentration of 55 vol%. The electric breakdown strength of the nanocomposite is greatly enhanced to 336 MV/m at BT concentration of 10 vol% and the calculated energy density is 6.8 J/cm³. The results indicate that using PVP as surface modification agent can greatly enhance the dielectric permittivity and electric breakdown strength of the ceramic–polymer nanocomposite and achieve high-energy density for energy storage and power capacitor applications.

This article reports on research into the use of solid alkalis (Na₂CO₃ and K₂CO₃) as activators to obtain hybrid cement (cement whose hydration generates a mix of C–A–S–H and (N,C)–A–S–H gels) from a blend of 20% clínker + 40% blast furnace slag + 40% metakaolin. More specifically, the study aimed to determine the effect of activator dosage (5 and 8 wt%) and type of alkaline cation (Na⁺ or K⁺) on the 2- and 28-d mechanical strength of the end materials. The findings showed that the highest mechanical strength values were obtained with 5% Na₂CO₃. According to the XRD, NMR, and SEM/EDX analyses conducted on the reaction products, the alkalinity and solubilized chemical species generated by adding 5% Na₂CO₃ to the system yielded a mix of (N,C)–A–S–H and C–A–S–H cementitious gels as the main reaction products. The secondary reaction products included metastable (3CaO·Al₂O₃·CaCO₃·11H₂O-type) carboaluminates that evolved into the calcite or vaterite forms of calcium carbonate. When K₂CO₃ was used (instead of Na₂CO₃), a (3CaO·Al₂O₃·0.5Ca(OH)₂·0.5CaCO₃·11H₂O-type) hemicarboaluminate also formed. The study also revealed that Na⁺ favors coagulation/precipitation more effectively than K⁺, generating gels with a wider range of Qⁿ species.

The rheology of inkjet printing inks must be well controlled in order to be able to form small droplets. One solution is to use low volume fraction dispersed suspensions, but this leads to a common problem during drying called the coffee stain effect. It is caused by particle migration from the center to the edge of a drying drop and leads to nonuniform printed structures. This article describes an approach, to suppress the coffee stain effect by a sufficiently fast increase in viscosity after deposition. Due to the viscosity limitations during printing, inks with tailored rheology and drying behavior need to be developed. Ceramic inks were prepared and printed. First, a binder was added to study the influence of viscosity on printability and the coffee stain effect. Second, the use of a high vapor pressure solvent for faster drying was investigated. Eventually, an ink with the combination of binder and fast drying agent was prepared. This ink showed a considerable decrease in drying time as well as a rapid increase in viscosity after deposition and was suitable to completely suppress the coffee stain effect. Plateau-like structures were achieved by adapting the drying temperature to permit particle movement to a certain degree.

The use of RE₂Si₂O₇ materials as environmental barrier coatings (EBCs) and in the sintering process of advanced ceramics demands a precise knowledge of the coefficient of thermal expansion of the RE₂Si₂O₇. High-temperature X-ray diffraction (HTXRD) patterns were collected on different RE₂Si₂O₇ polymorphs, namely A, G, α, β, γ, and δ, to determine the changes in unit cell dimensions. RE₂Si₂O₇ compounds belonging to the same polymorph showed, qualitatively, very similar unit cell parameters behavior with temperature, whereas the different polymorphs of a given RE₂Si₂O₇ compound exhibited markedly different thermal expansion evolution. The isotropy of thermal expansion was demonstrated for the A-RE₂Si₂O₇ polymorph while the rest of polymorphs exhibited an anisotropic unit cell expansion with the biggest expansion directed along the REO_x polyhedral chains. The apparent bulk thermal expansion coeficcients (ABCTE) were calculated from the unit cell volume expansion for each RE₂Si₂O₇ compound. All compounds belonging to the same polymorph exhibited similar ABCTE values. However, the ABCTE values differ significantly from one polymorph to the other. The highest ABCTE values correspond to A-RE₂Si₂O₇ compounds, with an average of 12.1 × 10⁻⁶ K⁻¹, whereas the lowest values are those of β- and γ-RE₂Si₂O₇, which showed average ABCTE values of ~4.0 × 10⁻⁶ K⁻¹.

Titania thin films with ordered nanostructures are of general interest in fields of photocatalysis, gas sensors, energy storages, energy conversions, etc. In this study, we report a low-temperature crystallization and the simultaneously occurred morphology change of titania thin films in a dilute H₂SO₄ solution. Amorphous titania nanowire arrays were fabricated by a Ti–H₂O₂ interaction, which transformed to crystallized nanoflower arrays through a dissolution–precipitation route during the subsequent acid treatments. The nanoflowers were doped with nitrogen and also incorporated with sulfate ions. An increasing H₂SO₄ concentration resulted in larger nanoflowers with higher anatase content; but the crystallinity reduced. The low-temperature-derived nanoflower arrays possessed high density of surface hydroxyl groups and defect V_O-Ti³⁺ sites, which contributed to a high absorption and enhanced photodegradation efficiency of rhodamine B in water under the illumination of UV–visible light during the first several runs of photocatalytic evaluations. The beneficial surface defects diminished gradually with increasing runs; however, the average reaction rate constants of the acid treated films are still superior to that of the calcinated one, which can be attributed to several structural parameters such as the nanoflower morphology, incorporation of sulfate ions, and the coexistence of anatase and rutile.

Ceramics of La_xSr_1−xNb_yTi_1−yO₃ (LSNT) were synthesized under various reducing atmospheres. Covering the specimens with graphite carbon felt under an Ar-gas flow during sintering drastically enhanced the electrical conductivity, σ. Ti K-edge absorption spectra indicated the presence of Ti³⁺ for heavily reduced specimens. The increase in conductivity was attributed to the 3d band of Ti³⁺. The maximum value for the figure of merit, ZT, was obtained for strontium titanate ceramics modified with both 5 mol% La and 5 mol% Nb, namely 5/5-LSNT, exhibiting a ZT value of ~0.221 at 473 K. This high ZT value was almost 1.5 × larger than that of the conventional 10 mol% La-doped sample, 10/0-LSNT (ZT~0.144), and was mainly attributed to the larger Seebeck coefficient of the material.

Substituting silicon by transition metals in polymer-derived ceramics (PDCs) holds the potential for a new class of polymer-derived ceramics for ultrahigh-temperature structural applications. We present experiments that show that the solid solubility of HfO₂ extends to Hf/Si ratio of <0.22. The materials are synthesized from (miscible) organic precursors. Similar to silicon-based materials they remain amorphous after pyrolysis at 1000°C. Small-angle X-ray scattering and Raman spectra remain essentially unaltered. It is postulated that Hf, like Si, forms mixed-bond tetrahedra with C, O, and N. The difference in the enthalpy of Hf-based, and Si-centered tetrahedra is calculated using single-bond energies, reinforcing the feasibility of substituting Si with Hf or with Zr atoms. Such polymer-based HfSiCNO compounds made directly from liquid organics, by a simple manufacturing process, may also be relevant to nanoscale dielectrics with low leakage electric charge in microelectronics applications.

This study investigates the effects of doping BaTiO₃ with MgO and Y₂O₃ on the formation of core–shell structure. The MgO and Y₂O₃ enhanced the shrinkage upon sintering and inhibited the grain growth, respectively. However, increasing the amount of Y₂O₃ to 3.0 mol% suppressed the shrinkage upon sintering. The results of the diffusion experiment revealed that Y³⁺ was dissolved in the BaTiO₃ lattice to a depth of 5–10 nm inside the grains, whereas Mg²⁺ tended to remain close to the surfaces of the grains when sintered at 1150°C for 18 h, suggesting that Y³⁺ may have had a higher diffusion rate than Mg²⁺. The Mg²⁺ prevented the diffusion of Y³⁺ into the core during sintering. Therefore, Mg²⁺ plays an important role as a shell maker in the formation of the core–shell structure in the codoped system. The core–shell structure can be obtained in BaTiO₃ ceramics that are codoped with MgO and Y₂O₃ upon sintering at 1150°C for 3 h.

A 3Y-TZP/Nb composite fabricated by Hot-pressing (HP) sintering with well-distributed lamellar/flake–shaped metal particles (20 vol% fraction) has been studied under cyclic loading. Fatigue life was determined for the ceramic/metal composite as well as for monolithic zirconia to compare the sensitivities of both materials to cyclic stresses. In both cases, the fatigue test was performed according to ISO 6872. It was found that the 3Y-TZP/Nb composite exhibits fatigue behavior which was compared with monolithic zirconia. The growth of fatigue cracks influences the bridging actions of the metallic grains and causes significant degradation in the mechanical properties of the composite material.

Controlling the morphological structure of titanium dioxide (TiO₂) is crucial for obtaining superior power conversion efficiency for dye-sensitized solar cells. Although the sol–gel-based process has been developed for this purpose, there has been limited success in resisting the aggregation of nanostructured TiO₂, which could act as an obstacle for mass production. Herein, we report a simple approach to improve the efficiency of dye-sensitized solar cells (DSSC) by controlling the degree of aggregation and particle surface charge through zeta potential analysis. We found that different aqueous colloidal conditions, i.e., potential of hydrogen (pH), water/titanium alkoxide (titanium isopropoxide) ratio, and surface charge, obviously led to different particle sizes in the range of 10–500 nm. We have also shown that particles prepared under acidic conditions are more effective for DSSC application regarding the modification of surface charges to improve dye loading and electron injection rate properties. Power conversion efficiency of 6.54%, open-circuit voltage of 0.73 V, short-circuit current density of 15.32 mA/cm², and fill factor of 0.73 were obtained using anatase TiO₂ optimized to 10–20 nm in size, as well as by the use of a compact TiO₂ blocking layer.

Single additives (Y₂O₃, MgO, and Al₂O₃) were used as sintering aid of Si₃N₄. The density, crystal phase, microstructure, transmittance, hardness, and fracture toughness of sintered Si₃N₄ were investigated. Highly densified sintered bodies were obtained in single Y₂O₃ and MgO systems, but not in single Al₂O₃ system. The XRD results indicated that sintered bodies were composed of β-Si₃N₄. The SEM images showed that all the sintered bodies had a fine-grained microstructure with an average diameter of 0.29–0.37 μm. The thickness of grain boundary was changed with additive content. The transmittance (T) and the wavelength (λ) followed the relationship of T∝ exp(−λ^−2.3) due to the light scattering. The transmittance was mainly influenced by the refractive index of additives and the thickness of grain boundary phase. The hardness and fracture toughness of sintered ceramics were 12.6–15.5 GPa and 6.2–7.2 MPam^1/2, respectively.

For the first time we have demonstrated the densification of high-purity nanostructured (d_avg ≈ 60 nm) tungsten carbide by High Pressure Spark Plasma Sintering (HPSPS) in the unusually low temperature range of 1200°C–1400°C. The high-pressure sintering (i.e., 300 MPa) produced dense material at a temperature as low as 1400°C. In comparison with more conventional sintering techniques, such as SPS (80 MPa) or hot isostatic pressing, HPSPS lowered the temperature required for full densification by 400°C–500°C. High Pressure Spark Plasma Sintering, even in absence of any sintering aid or grain growth inhibitor, retained a very fine microstructure resulting in a significant improvement in both hardness (2721 HV₁₀) and fracture toughness (7.2 MPa m^1/2).

Mesoporous γ-Al₂O₃ powders with nanofiber and nanorod-like structures were synthesized using boehmite sols in the presence of triblock copolymer, P123 in ethanol by solvothermal process at different temparatures (100°C–165°C) followed by calcination at 400°C–1000°C. The powders were characterized by low- and wide-angle X-ray diffraction (XRD), N₂ adsorption–desorption, and transmission electron microscopy (TEM). The adsorption efficiency of the powders with Congo red (CR) was studied by UV–vis spectroscopy. The γ-Al₂O₃ phase became stable up to 1000°C. The nanorods obtained at 165°C had narrower pore size distribution (PSD) than nanofibers synthesized at 100°C, the former showed higher CR adsorption efficiency. The stepwise growth mechanism of nanofibers to nanorods conversion with increase in solvothermal temperatures was illustrated.

Highly thermal stable Si–N-doped BAM (BaMgAl₁₀O₁₇: Eu²⁺) phosphors have been successfully synthesized by a mechanochemically assisted solid-state reaction method. Mechanical milling greatly improved the amount of Si–N pairs substituted for Al–O pairs in BAM lattice>. Si–N incorporation improves the photoluminescence (PL) properties and the color purity, reduces the thermal quenching, and most importantly, increases the thermal stability of the BAM phosphors significantly. The interpretation of the positive influence of Si–N doping was attributed to the local structure of the produced phosphors, which was analyzed with the aid of first-principles density functional calculations. This analysis showed that the substitution of Al–O pairs with Si–N pairs should preferentially occur in the boundary between the spinel layer and the conduction layer of the BAM phosphor, leading to a compression of the conduction layer. Eu²⁺ ions prefer to substitute the N-coordinated Ba²⁺ ions in the lattice of Si–N-doped BAM phosphors, leading to a strong Eu–N bonding. The results of these calculations agree fairly well with the results recorded experimentally, specifically the electron paramagnetic resonance (EPR) spectra, the X-ray absorption fine structure (XAFS), thermoluminescence spectra (TL), and decay behaviors.

Anodic coagulation casting of fibrinogenic ceramic suspensions is a novel processing technology, which is based on the electrically induced transformation of the water soluble fibrinogen into the insoluble fibrin. Contrary to the direct coagulation casting (DCC) technology, green formation does not depend on a pH-shift and as the fibrin coagulate forms on an anode, it can be combined with the electrophoretic deposition (EPD) technology.

A CaO–Al₂O₃–SiO₂ (CAS)-based glass interlayer was developed for joining of porous alumina membrane tubes with dense alumina in this work. The results indicated that the interfacial microstructure of the joint was highly sensitive to the quench rate from the joining temperature, which rendered crystallization of CaTiSiO₅ at a fast quench rate but CaAl₂Si₂O₈ at a slow quench rate due to the interfacial reaction between the CAS glass interlayer and the substrate. An extra crystallization treatment during quench, i.e., dwelling at 800°C–900°C for 2 h, produced a multiphase interlayer consisting of LiAlSi₂O₆, CaTiSiO₅, and CaAl₂Si₂O₈. All joints were evaluated by the thermal shock test. The results showed that the LiAlSi₂O₆-containing joint interlayer had much lower thermal shock resistance than those without LiAlSi₂O₆.

The thermoelectric properties of bulk polycrystalline Sr_0.5Ba_0.5Nb₂O₆ (SBN50) fabricated via solution combustion synthesis (SCS) and reduced at temperatures of 900°C–1150°C were explored. The Seebeck coefficient (S) of all samples increased over the entire range of testing temperatures; a peak S value of −281 μV/K was obtained at 930 K for the sample reduced at 900°C. A metal-insulator transition was observed in the electrical conductivity (σ) of samples reduced at 1000°C–1150°C, whereas only semiconducting electrical behavior was observed for the sample reduced at 900°C. An optimal balance between S and σ was achieved for the pellet reduced at 1000°C, which exhibited a maximum power factor of 1.78 μW/cm·K² at 930 K. Over a temperature range of 300–930 K, the thermal conductivity (κ) of as-processed and reduced (1000°C) SBN50 was found to be 1.03–1.4 and 1.46–1.84 W/m·K, respectively. A maximum figure of merit (ZT) of 0.09 was obtained at 930 K for the 1000°C-reduced sample. X-ray photoelectron spectroscopy revealed that the Nb²⁺ peak intensity increased at higher reduction temperatures, which could possibly lead to a distortion of NbO₆ octahedra and a decrease in the Seebeck coefficient.

Controlling residual amount of defects in transparent ceramics is a major challenge for laser applications. This study was focused on microstructural evolution of Nd:YAG ceramics during their reactive solid-state sintering which was correlated to their optical transmittance. From microstructural observations, the microstructural maps and grain size-density and grain size-pore size sintering trajectories of Nd:YAG ceramics were established as a function of silica content. For densities higher than 99.7%, the occurrence of intragranular porosity was correlated to a critical pore radius of 0.16 μm. Silica appears to favor the formation of intragranular porosity which was attributed to the increasing of the grain growth rate compared with the densification one. An analytical model was established by coupling the analytical laws derived from sintering trajectories and the classical theory of light diffusion, allowing to correlate the microstructural features of transparent Nd:YAG ceramics to their optical properties.

The effects of MgO doping and specific surface area of powder on microwave sintering behavior of α-Al₂O₃ were investigated. A comparative study was simultaneously achieved in conventional and microwave heating with an identical thermal process. The experimental results show that both MgO and particle size have significant influence on microwave enhancement in the densification of the alumina samples. It is found that an amount of MgO surrounding the solubility limit in Al₂O₃ or leading to second phase precipitation of MgAl₂O₄ spinel induces more significant microwave enhancement. A significant microwave gain in densification is also observed while powder has a high specific surface area. These results indicate that the enhancements during microwave sintering processes are associated with the formation of lattice defect and with the increase in concentration of grain-boundary region.

The large bulk high-T_c YBa₂Cu₃O_7−x (YBCO) superconductor samples were prepared by plastic-forming method. We examined the effects of the solvent and the crystallinity of YBCO powder on the composition, crystallinity, and superconducting properties of YBCO sheet samples (sample size: 50 mm × 50 mm× 3 mm). By changing the solvent from water to turpentine oil, the leaching of Ba²⁺ ions from YBa₂Cu₃(OH)_y multimetallic hydroxide particles used as an inorganic binder and the YBCO powder were reduced. This results in the composition of the grain boundaries of fired YBCO sheet samples to be the same as the composition of YBa₂Cu₃(OH)_y multimetallic hydroxide particles. Changing nondoped YBCO powder prepared by sintering to 5 wt% Pt-doped YBCO powder prepared by melt texturing, J_c value of YBCO sheet samples changed from about 700 to 6,106 A/cm² at 77 K.

A combustion synthesis method has been developed for synthesis of Eu²⁺-doped Ca₂Si₅N₈ phosphor and its photoluminescence properties were investigated. Ca, Si, and Eu₂O₃ powders were used as the Ca, Si, and Eu sources. NaN₃ and NH₄Cl were found necessary to be added for the formation of the product phase and addition of Si₃N₄ was found to enhance the product yield. These powders were mixed and pressed into a compact, which was then wrapped up with an igniting agent (Mg + Fe₃O₄). The reactant compact was ignited by electrical heating under a N₂ pressure of 0.7 MPa. Effects of these experimental parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized Ca₂Si₅N₈: Eu²⁺ phosphor absorbs light in the region of 300–520 nm and shows a broad band emission in the region of 500–670 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺. Eu₂O₃ was found partially unreacted and a certain amount of oxygen is believed to be incorporated into the lattice of the product phase. The peak emission intensity (~93% of a commercially available phosphor, YAG:Ce³⁺v) and the peak emission wavelength (571–581 nm) were found to be lower and shorter, respectively, than that reported in the literature. These are considered to be mainly due to oxygen incorporation, which not only reduces nephelauxetic effect and crystal field splitting but also causes a lowering of internal quantum efficiency.

The Microstructure and microwave dielectric properties of Bi₂O₃-deficient Bi₁₂SiO₂₀ ceramics were investigated. A small amount of unreacted Bi₂O₃ phase melted during sintering at 825°C and assisted with densification and grain growth in all samples. The melted Bi₂O₃ reacted with remnant SiO₂ during cooling to form a Bi₄Si₃O₁₂ secondary phase. The nominal composition of Bi_11.8SiO_19.7 ceramics sintered at 825°C for 4 h had a high relative density of 97% of the theoretical density, and good microwave dielectric properties: ε_r = 39, Q × f = 74 000 GHz, and τ_f = −14.1 ppm/°C. Moreover, this ceramic did not react with Ag at 825°C.

Niobium-doped Titanium dioxide (Nb:TiO₂) transparent films were successfully deposited on glass substrates using a non-aqueous sol-gel spin coating technique. The effect of Nb concentration on the structural and photocatalytic properties of Nb:TiO₂ films was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV visible spectroscopy. The films with 12 at.% (atomic percent) Nb doped TiO₂ showed excellent photocatalytic activity through 97.3% degradation of methylene blue (MB) after 2 h of UV irradiation.

Aluminum oxynitride spinel (AlON) powders were synthesized by aluminothermic reaction in a reducing N₂-CO atmosphere. Low cost and easily available aluminum and γ-Al₂O₃ alumina micrometer-sized powders were employed as starting materials. Mixed powders consisting of 75 wt% Al and 25 wt% Al₂O₃ were milled together and pressed into billets with diameter of 20 mm and height of 15 mm. Green-body billets were then calcined in charcoal-protected condition (namely in a N₂-CO atmosphere) at 1600°C. Phase composition and microstructure of final sintered products were analyzed. The results showed that AlON phase with AlN as a minor phase was formed at 1600°C for 3 h. At the same time, grains of AlON were tabular in shape and whiskers can be found in samples after being sintered at 1600°C.

Rare–earth-doped strontium titanate ceramics yielding the formula Re_0.02Sr_0.97TiO₃ (Re–ST, Re = La, Sm, Gd, Er) were prepared by solid-state reaction route. All Re–ST ceramics had single cubic perovskite structure similar to pure SrTiO₃ (ST). The grain size of Re–ST ceramics dramatically decreased to 1–10 μm, depending on different rare-earth elements, as compared to ~30 μm of pure ST. The relative dielectric constant of Re–ST ceramics (ε_r = 2750–4530 at 1 kHz) showed about 10–15 times higher than that of pure ST (ε_r = 300 at 1 kHz), whereas the dielectric loss of Re–ST ceramics still remained lower than 0.03 (at 1 kHz) at room temperature. Under 0–1.63 × 10⁶ V/m bias electric field testing conditions, the ε_r of Re–ST ceramics at room temperature changed within 14%. The P–E results indicated that the Re–ST ceramics were linear dielectrics. Together with their relatively high breakdown strength (E_b > 1.4 × 10⁷ V/m), the Re–ST ceramics could be very promising for high-voltage capacitor applications. Meanwhile, the temperature stability of the ε_r of Re–ST ceramics was evaluated in a temperature range of −60°C–200°C.

Highly crystalline and monophasic nanoparticles of In_2−xCo_xO₃ (0.05 ≤ x ≤ 0.15) were successfully synthesized by the solvothermal method through an oxalate precursor route. Collective evidence from X-ray diffraction and reflectance measurements suggest that the Co²⁺ is incorporated into the In₂O₃ lattice site. Effect of cobalt dopant on the growth and morphology of indium oxide was studied by transmission electron microscopy. It has been observed that particle size decreases from 23 to 9 nm on increasing the Co concentration. High surface area has been obtained, with values ranging between 66 and 151 m²/g, respectively. Values for the dielectric constant were around 40. All these solid solutions show paramagnetic behavior with weak antiferromagnetic interactions.

In this work, we demonstrate that the martensitic t → m phase transformation of ZrO₂ powder stabilized with Eu³⁺ and Eu³⁺/Y³⁺ ions, can be effectively monitored by photoluminescence (PL) spectroscopy. As the luminescent properties of Eu³⁺ from within a host lattice are strongly influenced by the coordination geometry of the ion, we used the emission spectrum to monitor structural changes of ZrO₂. We synthesized Eu³⁺-doped and Eu³⁺/Y³⁺-codoped samples via the coprecipitation method, followed by calcination. We promoted the martensitic transformation by applying mechanical compression cycles with an increasing pressure, and deduced the consequential structural changes from the relative intensities of the ⁵D₀ → ⁷F₂ hypersensitive transitions, centered, respectively, at 606 and 613 nm whether the Eu³⁺ is in the eightfold coordinated site of the tetragonal phase or in the sevenfold coordinated site of the monoclinic phase. We suggest that the unique emission profile for Eu³⁺ ions in different symmetry sites can be exploited as a simple analytical tool for remote testing of mechanical components that are already mounted and in use. The structural changes observed by PL spectroscopy were corroborated by X-ray powder diffraction (XRPD), with the phase compositions and volume fractions being determined by Rietveld analysis.

Dense cordierite ceramics were prepared from a sol mixture of alumina, silica, and magnesia, and the relationship between microstructure and thermal expansion was clarified for sinters with relative density greater than 97%. In the dense cordierite ceramics, submicrometer-sized primary cordierite crystals aligned in the same crystal orientation and constituted the domain structure. We discovered that these domain structures could be easily observed by optical polarizing microscopy and quantified by digital image analysis of the photographs. The occurrence of microcracks between domains larger than 40 μm was induced by the thermal expansion anisotropy of the cordierite crystal axes. As a result, the mean thermal expansion coefficient of the cordierite ceramics decreased to 0.4 × 10⁻⁶ K⁻¹ from the average value of the crystal axes of 1.7 × 10⁻⁶ K⁻¹. This lower thermal expansion coefficient could be theoretically explained by partial microcracking.

A variety of multiseeding techniques have been investigated over the past 20 yr in an attempt to enlarge bulk (RE)BCO superconducting samples fabricated by the top-seeded melt growth (TSMG) process for practical applications. Unfortunately, these studies have failed to establish whether technically useful values of trapped field can be achieved in multiseeded bulk samples. In this work specially designed, 0°–0° and 45°–45° bridge seeds of different lengths have been employed to produce improved alignment of the seeds during the TSMG process. The ability of these bridge-seeded samples to trap magnetic field, which is the key superconducting property for practical applications of bulk (RE)BCO, is compared for the samples seeded using 0°–0° and 45°–45° bridge seeds of different lengths. The grain boundaries produced by these bridge seeds are analyzed in detail, and the similarities and differences between the two bridge-seeding processes are discussed.

This article reports a comparative characterization of ultrafine MgAl₂O₄ spinel nanoparticles synthesized by polymeric precursor (Pechini) and coprecipitation methods. The nanoparticles were evaluated in terms of purity and surface cleanliness, size distribution, state of agglomeration, and sintering behavior. Powders synthesized by the Pechini technique were highly agglomerated and revealed a bimodal particle size distribution centered around 12 and 27 nm. Thermal analysis and infrared spectroscopy measurements indicated that carbon species remained on the surface of the powders only to be released when temperatures exceeded 1000°C. Isothermal sintering of such nanopowders at 1300°C showed a maximum relative density of only 54%. MgAl₂O₄ synthesized via coprecipitation created small nanoparticles, around 5–6 nm after calcination at 800°C, with significantly less agglomeration. Compared with the precursor-derived powders, excellent sinterability of the coprecipitated powders was obtained under the same sintering conditions. Relative densities above 90% were obtained after only 10 min, which further increased to greater than 95% after 20 min with no sintering aids or dopants. The results highlight the importance of purity and processing control to exploit the beneficial high sinterability of nanoparticles.

It is of great importance to discover completely the correlation between the defects and positron lifetimes in positron annihilation technology (PAT) and reveal clearly the effect of defects on the dielectric constant of universal microwave ceramics. In this work, ZnNb_2−xTi_xO_6−x (0 ≤ x ≤ 0.5) dielectric ceramics with nonstoichiometric defects were prepared by solid-state reaction. All the pores and defects in as-prepared ceramics were accurately revealed by PAT as a convenient way. The positron lifetimes of τ₃ and τ₂ in positron annihilation lifetime spectra (PALS) were dependent on two kinds of pores correlated with where o-Ps atoms and trapping positron annihilated in, whereas τ₁ could be separated evidently into τ_b and τ_t which are related to bulk structure and negatively charged defects in the system. The dielectric constant of microwave ceramics ZnNb_2−xTi_xO_6−x, which increases from 26 to 49 with x increasing from 0 to 0.5 at 10 GHz, is confirmed to be directly controlled by the negatively charged defect of through cation rattling.

Lead tungstate PbWO₄ nanocrystals in transparent lead borate glass-ceramics containing Er³⁺ ions were fabricated. Luminescence spectra at about 1530 nm due to main ⁴I_13/2–⁴I_15/2 laser transition of Er³⁺ ions were examined for glass samples before and after heat treatment. Near-infrared luminescence of Er³⁺ ions in glass-ceramics is enhanced and long-lived in comparison to precursor glasses. It suggests that the Er³⁺ ions are partially incorporated into PbWO₄ crystalline phase.

Using a conventional solid-state reaction Ca₅A₄(VO₄)₆ (A²⁺ = Mg, Zn) ceramics were prepared and their microwave dielectric properties were investigated for the first time. X-ray diffraction revealed the formation of pure-phase ceramics with a cubic garnet structure for both samples. Two promising ceramics Ca₅Zn₄(VO₄)₆ and Ca₅Mg₄(VO₄)₆ sintered at 725°C and 800°C were found to possess good microwave dielectric properties: ε_r = 11.7 and 9.2, Q × f = 49 400 GHz (at 9.7 GHz) and 53 300 GHz (at 10.6 GHz), and τ_f = −83 and −50 ppm/°C, respectively.

Ytterbium-doped Sr₅(PO₄)₃F transparent ceramics have been developed through spark plasma sintering (SPS) with a low sintering temperature and short dwelling time. The XRD patterns show a polycrystalline hexagonal phase, and the TEM microstructure characterization indicates that the ceramics have a narrow grain size distribution which ranges from 40 to 200 nm, with an average grain size around 150 nm. The transmittance of a 2 mm thick ceramic sample is measured to be 74% at 1000 nm by a UV–Vis–NIR spectrophotometer. Furthermore, there is a strong emission peak around 1040 nm which has a lifetime of 1.06 ms and is exhibited by a PL spectrometer with the 980 nm laser diode excitation.

Highly (100) oriented lead strontium titanate (Pb_0.4Sr_0.6TiO₃) thin films were deposited on LaNiO₃ -coated Si substrate via radio-frequency magnetron sputtering method with substrate temperature ranging from 300 to 500°C. The PST thin films were crystallized at a temperature as low as 300°C, which may result from the well-controlled stoichiometry and the in situ crystallization on seed layer. At an electric field of 400 kV/cm, high tunability of 43% and 57% can be achieved for PST films deposited at 300°C and 500°C, respectively. Moreover, the dielectric response shows weak frequency dependence and the loss factor stays relatively low. The results suggest that such films should be promising candidate for the microwave tunable devices compatible with the current Si technology.

A novel Y_3−xSi₆N₁₁: xCe³⁺ yellow phosphor was synthesized using the carbothermal reduction and nitridition method at 1550°C for 16 h in this letter. Photoluminescence spectra indicated that the phosphor showed broad excitation spectrum and had strong absorption in range of 350–450 nm. It also gave a broad emission band (Full width at half maximum = 153 nm) centered at 575 nm under 425-nm excitation. With increasing Ce³⁺ concentration, the strongest emission intensity was obtained at 5 mol% Ce³⁺ doping amount and a systematic redshift was observed as the Ce³⁺ concentration increased. The results indicate that this novel yellow phosphor is a promising candidate for using in blue-chip-excited white light–emitting diodes (LEDs).

In this research, hydrothermal-calcination route was applied to synthesize In₂O₃ nanoparticles for gas sensor application. Hydrothermal synthesis with duration of 5 h at 180°C resulted in In(OH)₃ nanorods. Then, in the calcination step, considering controlled rate of heating and temperature, In₂O₃ nanoparticles with rough surfaces were obtained. In the next step, these nanoparticles were deposited by low frequency AC electrophoretic deposition between the interdigitated electrodes to fabricate gas sensor. Deposition in the frequency of 10 kHz resulted in the chained nanoparticles in the interelectrode space. At the end, gas sensitivity measurements were conducted at 150°C–300°C and revealed that fabricated sensor had fast response and recovery times to NO₂ gas.

Al- and B-doped 3C–SiC ceramics were prepared by hot-pressing powder compacts containing submicrometer-sized β-SiC, precursors of 5 wt% nanosized β-SiC, and an optional additive (Al or B) in an Ar atmosphere. Electron probe microanalysis (EPMA) investigation on the obtained specimens revealed that a portion of the doped Al and B atoms substituted the zinc blende lattice sites. The temperature-dependent electrical resistivity data of the Al- and B-doped SiC specimens were measured in the 4–300 K range and compared with those of an undoped specimen. The Al- and B-doped SiC specimens exhibited resistivities that were as high as ~10³ Ω cm at room temperature and ~10⁵ and ~10⁴ Ω cm, respectively, below 100 K. These values are larger than those of the undoped SiC specimen by a factor of ~10⁴. Such high resistivities of the impurity-doped specimens are attributable to the carrier compensation by the Al- and B-derived acceptors located well above the valence-band edge of 3C–SiC. Photoluminescence investigation revealed that the Al- and B-doped specimens exhibited emission profile below 2 eV, implying the existence of the acceptors.

This study aims to understand the viscosity variation of amorphous materials, and hence establish a theoretical model for reliable applications. The investigation was carried out by simplifying an amorphous system to a mixture of many subsystems which switch their energy states and relaxation processes stochastically. The response of the macroscopic system is then treated as an ensemble average of relaxations of individual subsystems. Our derivation illuminates the transition from exponential to nonexponential relaxation and that the sudden increase of fragility in the viscosity–temperature relation with reducing temperature could be attributed to the bifurcation from the harmonic mean of the subsystems towards the arithmetic mean. The successful application of our model to the amorphous selenium indicates that the model captures the fundamental mechanism of viscosity variation.

Kaolinite–silica nanocomposites with a green porosity ranging from 75% to 87% were prepared using a freeze-casting technique. The initial solids loading values (kaolinite platelets plus silica nanospheres) greatly influence the sintering behavior as well as the phase and strength of the resulting porous composites. The composites with lower solids loading exhibit faster sintering (e.g., larger shrinkage, more extensive thickening of the pore walls) when sintered at 1250°C, which in turn, results in a rapid increase in flexural strength. All the composites maintain a high porosity (above 50%) after sintering at 1250°C for 72 h, whereas the flexural strength of the composites increases from roughly 0.2 MPa for the green samples to 13.3, 7.5, and 6.5 MPa for 12, 18, and 24 vol% solids samples, respectively, after sintering. It is believed that solids loading affects kaolinite–silica packing during the sol-to-gel transition as a minimum amount of silica nanoparticles is required to build the gel network. This particle packing difference influences the amount of kaolinite–silica interfacial contact, which in turn affects the strength. The strength increase through solids loading change is a combined effect of changes in the porous structure during sintering plus the development of a new phase at the silica–kaolinite interface.

Thorough elastic analysis of porous silicon carbide preforms fabricated using two different polymer waxes as pore formers is carried out. Both the amount and the mixture ratio of the waxes were varied to fabricate preforms with different pore morphologies and porosities in the range of 27–67 vol%. Results show that both the longitudinal and the shear elastic constants decrease with increasing porosity. The rate of decrease in the elastic constants follows a model based on minimum solid area up to an intermediate porosity level. Uniaxial pressure applied prior to cold isostatic pressing and sintering significantly reduces the stiffness along the press direction. For the same initial powder mixture type, the elastic anisotropy of the preforms increases with an increase in the applied uniaxial pressure. The extent of anisotropy is strongly dependent on both the SiC/wax ratio as well as the mixture ratio between the two wax types. At low pore volume fractions a higher volume content of the smaller diameter wax and at high pore volume fractions a higher volume content of larger diameter wax lead to preforms with lowest anisotropy. A map is finally proposed to describe the dependence of the preform elastic properties on the type of initial powder mixture used.

In this article, we report the substrate effect on ferroelectric and magnetic properties of epitaxial BiFeO₃-based thin films at room temperature. (La, Mn) cosubstituted BiFeO₃ (BFOLM) thin films were deposited on differently lattice mismatched single-crystal substrates to manipulate the strain states in the as-deposited films. All the films with 30-nm thick CaRuO₃ bottom electrodes exhibited highly epitaxial growth behavior with a slightly monoclinic distorted lattice structure while their strain states are drastically different as confirmed by X-ray reciprocal space mapping. These films possessed significantly different macroscopic ferroelectric properties with giant remanent polarization of 101 ± 2, 65 ± 2, and 48 ± 2 μC/cm² for the films grown on SrTiO₃, (La, Sr)(Al, Ta)O₃, and LaAlO₃, respectively. It is found that the room-temperature magnetic properties are also in accordance with their strain state, having a reciprocal relationship with polarization. For example, the enhanced magnetization is associated with the suppressed polarization and vice versa. The stain tunability of multiferroic properties in BFOLM thin films are presumably ascribed to the polarization rotation and oxygen octahedral tilts.

Two-step hydrothermal synthesis of platelike potassium sodium niobate (K, Na)NbO₃ (KNN) template particles was investigated. Platelike K₄Na₄Nb₆O₁₉·9H₂O (KNN-hydrate) particles were synthesized in 4 mol/L aqueous alkali at 150°C by the sodium dodecyl benzene sulfonate (SDBS) surfactant-assisted hydrothermal method, which were used as crystal nucleus in the second step of hydrothermal synthesis. The two-step synthesized KNN-hydrate particles with 0.6 μm thickness and 7 μm width were prepared at 80°C after 10 h of the second step. After calcination of the KNN-hydrate particle at 600°C, platelike KNN particles were obtained, which were used as templates for textured ceramics. Particles obtained by the two-step synthesis showed regular morphology and uniform distribution, with a marked improvement in grain size.

Silicon carbide is a candidate cladding for fission power reactors that can potentially provide better accident tolerance than zirconium alloys. SiC has also been discussed as a host matrix for nuclear fuel. Chemical vapor–deposited silicon carbide specimens were exposed in 0.34–2.07 MPa steam at low gas velocity (~50 cm/min) and temperatures from 1000°C to 1300°C for 2–48 h. As previously observed at lower steam pressure of 0.15 MPa, a two-layer SiO₂ scale was formed during exposure to these conditions, composed of a porous cristobalite layer above a thin, dense amorphous SiO₂ surface layer. Growth of both layers depends on temperature, time, and steam pressure. A quantitative kinetics model is presented to describe the SiO₂ scale growth, whereby the amorphous layer is formed through a diffusion process and linearly consumed by an amorphous to crystalline phase transition process. Paralinear kinetics of SiC recession were observed after exposure in 0.34 MPa steam at 1200°C within 48 h. High-pressure steam environments are seen to form very thick (10–100 μm) cristobalite SiO₂ layers on CVD SiC even after relatively short-term exposures (several hours). The crystalline SiO₂ layer and SiC recession rate significantly depend on steam pressure. Another model is presented to describe the SiC recession rate in terms of steam pressure when a linear phase transition k_l governing the recession kinetics, whereby the reciprocal of recession rate is found to follow a negative unity steam pressure power law.

Spinel ZnGa₂O₄ ceramics were synthesized by conventional solid-state method and their microwave dielectric properties were investigated. The phase evolution and microstructures of specimens were studied by XRD and SEM. The textured surface microstructures of ZnGa₂O₄ ceramics formed at high sintering temperatures. The spinel-structured ZnGa₂O₄ ceramics sintered at 1385°C exhibited excellent microwave dielectric properties: a dielectric constant (ε_r) of 10.4, a quality factor (Q × f) of 94.600 GHz, and a temperature coefficient of resonant frequency (τ_f) of −27 ppm/°C. ZnGa₂O₄ ceramics have a low sintering temperature, a wide temperature region, and a small negative τ_f value. They are promising candidate materials for millimeter-wave devices.

This article studies the thermal shock resistance behavior of ceramic foams under sudden thermal load induced by a sudden temperature variation. Two types of thermal shock loading conditions are considered: cold shock and hot shock. Variations of the stress and stress intensity factor with thermal shock time, location, crack size, medium thickness, and relative density of the ceramic foam are given. Crack growth behavior is studied and crack growth velocity is explained from energy equilibrium consideration. The thermal shock resistances of ceramic foams are established from the view points of energy criterion and fracture mechanics concept.

Effects of Mg substitution on order/disorder transition, microstructure, and microwave dielectric characteristics of Ba((Co_0.6Zn_0.4)_1/3Nb_2/3)O₃ complex perovskite ceramics have been investigated. The ordered complex perovskite solid solutions are obtained in Ba((Co_0.6−x/2Zn_0.4−x/2Mg_x)_1/3Nb_2/3)O₃ ceramics (x = 0, 0.1, 0.2, and 0.3), and the ordering degree in the as-sintered dense ceramics increases with increasing Mg-substitution amount. The significantly improved Qf value is obtained in the present ceramics with increasing x, whereas the dielectric constant decreases slightly together with some increase of temperature coefficient of resonant frequency. The best combination of microwave dielectric characteristics is obtained in the composition of x = 0.3: ε_r = 33.7, Qf = 93 800 GHz, and τ_f = 9.6 ppm/°C. In the Mg-substituted compositions, clear domain boundaries are obtained and the domain size increases as x increases, the highest Qf value is obtained when the domain size is about 40–60 nm in the ceramics with x = 0.3. The increased ordering degree and the fine ordering domain structure are considered to primarily contribute to the significant increase of Qf value in the Mg-substituted Ba((Co_0.6Zn_0.4)_1/3Nb_2/3)O₃ complex perovskite ceramics.

Er³⁺/Yb³⁺/Li⁺-tridoped Y₂Ti₂O₇ nanophosphors were synthesized via a facile sol–gel process. The samples were characterized by the inductively coupled plasma atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared-to-visible upconversion (UC) luminescence spectra. XRD analysis showed that the crystallization temperature of pyrochore-type Y₂Ti₂O₇ was reduced due to the flux effect of Li⁺ ions, whereas TEM measurements confirmed that the particles size of (Y_0.815Er_0.01Yb_0.075Li_0.10)₂Ti₂O₇ was about 30–40 nm when calcining at 800°C for 1.0 h. The calcining temperature and Li⁺ ion concentration dependence on UC luminescence spectra were investigated. It was found that, when incorporating 10.0 mol% Li⁺ ion, the UC red and green emission intensity was drastically increased by a factor of 18.6 and 8.3, respectively. The enhancement of UC emission may be mainly attributed to the modification of local symmetry around Er³⁺ ions by tridoping Li⁺ ions. And also, the pump power dependence of the emission intensity was investigated to understand the fundamental UC mechanism.

Group VIII metal oxides, that is, Fe₂O₃, Co₂O₃, and NiO have been introduced to 0.2Pb(Zn_1/3Nb_2/3)O₃–0.8Pb(Zr_0.50Ti_0.50)O₃ (PZN–PZT) to deterministically identify the substitution mechanism and meantime to tailor mechanical and piezoelectric properties in obtaining energy harvesting materials. On the basis of the X-ray diffraction and Raman analysis, it is clear that the group VIII metal oxides induce a phase transformation from the morphotropic phase boundary to the tetragonal phase side, and the corresponding grain size increases accordingly. It is reasonable to deduce that two types of substitution behaviors coexist in the group VIII metal oxides added PZN–PZT system. Due to the mixed valence of +2 and +3, the foreign doping ions prefer to enter the B site in the perovskite structure, not only substituting for Ti⁴⁺, Zr⁴⁺, and Nb⁵⁺ ions in the inequivalence replacement but also substituting for Zn²⁺ ions in the equivalence replacement. The proposed complex substitution mechanisms can give the full explanation about the grain growth phenomena and the variation in mechanical and electric properties in the modified PZN–PZT system. At the same doping level of 0.3 mol%, the maximum transduction coefficient (d₃₃·g₃₃ = 13120 × 10⁻¹⁵ m²/N) and good fracture toughness (K_IC = 1.32 MPa m^1/2) are obtained in Co₂O₃ added 0.2PZN–0.8PZT ceramics, which shows great promise as practical materials for energy harvesting device applications.

Ba₈CuTa₆O_24−δ ceramics possess exceptionally high microwave dielectric loss among the eight-layer twinned hexagonal perovskite Ba₈MTa₆O₂₄ (M = Zn, Co, Ni, Mg, Cu) analogs. Impedance spectroscopy measurement demonstrates that the eight-layer Ba₈CuTa₆O_24−δ ceramics show the electrical heterogeneous microstructure, consisting of leaky insulating grains and more resistive grain boundary regions. This induced internal barrier layer capacitance (IBLC) effects on Ba₈CuTa₆O_24−δ ceramics. The heterogeneous electrical microstructure is associated with partial reduction of Cu²⁺ to Cu⁺ and oxygen loss during the sintering procedure and limited reoxidization along grain boundary regions on cooling. The existence of Cu⁺ in Ba₈CuTa₆O_24−δ ceramic is confirmed by X-ray photoelectron spectroscopy measurement. The leaky insulating bulk property for the Ba₈CuTa₆O_24−δ ceramics is compared with the highly insulating bulk behavior of other low dielectric loss analogs, which indicates that the significant defects of Cu⁺ and oxygen vacancies are responsible for the high microwave dielectric loss of the Ba₈CuTa₆O_24−δ ceramics.

HfC-30 vol%SiC ceramics with a relative density of 99.7% was obtained by pressureless sintering at 2300°C for 0.5 h. The resultant ceramics showed fine microstructure with HfC grain size around 1 μm. The hardness (20.5 ± 0.2 GPa), bending strength (396 ± 56 MPa), and fracture toughness (2.81 ± 0.18 MPa·m^1/2) of HfC-30 vol%SiC ceramics were at least 20% higher than those of monolithic HfC ceramics. The influences of SiC particle size, volume fraction, and the oxide impurity on the microstructure evolution of HfC-based ceramics were examined. The results indicate that SiC addition and the oxygen impurity introduced by ball milling play opposite roles in the HfC grain growth during sintering. The oxide impurity introduced by ball milling caused the HfC grain coarsening, whereas SiC particles inhibited the grain growth of HfC significantly.

Atomistic simulation techniques are used to examine the stability of Ruddlesden–Popper (R–P) phases Sr(n = 1, 2, 3, 4 and ∞). Various sets of empirical pair potentials are employed to determine the formation energies of the R–P phases. Formation energies are also calculated with Density Functional Theory (DFT). The tendency of a given R–P phase to dissociate into a lower order R–P phase plus SrTiO₃ perovskite is found to increase with increasing n. The results obtained are compared with experiment and previous computational studies. The stability of intergrowth phases with respect to the pure R–P compounds is examined. In all cases the intergrowths are calculated to be thermodynamically less stable than the pure R–P phase, but the differences are in some cases negligible. Finally, the energy for SrO partial Schottky disorder in strontium titanate is computed taking the formation of R–P phases into account.

Preparation of LuFe₂O₄ ceramics under vacuum environment was investigated together with the structural, dielectric, and magnetic characterization. Single-phase LuFe₂O₄ could be obtained by the present process and the crystal structure was identified to be rhombohedral in space group . An obvious dielectric relaxation with activation energy of 0.29 eV was observed between 175 and 275 K. The Néel temperature of the present ceramics was ~250 K, and a reentrant spin glass transition was indicated at ~216 K. Two anomalies were observed in the DSC curve, which were relative with the ferrimagnetic transition and 2D–3D charge ordering transition of LuFe₂O₄. Meanwhile, a remarkable decrease appeared in the dielectric constant of the as-magnetized LuFe₂O₄ sample, implying the magnetodielectric effect in the present ceramics.

Silicon oxycarbides modified with main group or transition metals (SiMOC) are usually synthesized via pyrolysis of sol-gel precursors from suitable metal-modified orthosilicates or polysiloxanes. In this study, the phase composition of different SiMOC systems (M = Sn, Fe, Mn, V, and Lu) was investigated. Depending on the metal, different ceramic phases formed. For M = Mn and Lu, MO_x/SiOC ceramic nanocomposites were formed, whereas other compositions revealed the formation of M/SiOC (M = Sn), MSi_x/SiOC (M = Fe) or MC_x/SiOC (M = V) upon pyrolysis. The different phase compositions of the SiMOC materials are rationalized by a simple thermodynamic approach which generally correctly predicts which type of ceramic nanocomposite is expected upon ceramization of the metal-modified precursors. Calculations show that the thermodynamic stability of the MO_x phase with respect to that of the C–O system is the most important factor to predict phase formation in polymer-derived SiMOC ceramic systems. A secondary factor is the relative stability of metal oxides, silicates, carbides, and silicides.

Crystallized Lu–Si–O–N phases were believed to be the grain-boundary (GB) phases that might provide Si₃N₄ with excellent high-temperature mechanical properties. However, little is known about the intrinsic properties, as well as the synthesis, of the Lu–Si–O–N ceramics. This work reveals the reaction paths of heating Lu₂O₃, SiO₂, and Si₃N₄ powder mixtures (with the stoichiometry of 4:0.96:1) from room temperature to 1600°C. Thereafter, dense Lu₄Si₂O₇N₂ samples are synthesized by in situ reaction/hot-pressing method, and the mechanical properties at room temperature and elevated temperatures are reported for the first time. The Lu₄Si₂O₇N₂ samples show significant high-temperature mechanical properties, such as the elastic stiffness remains 77% from room temperature to 1500°C; and bending strength keeps 93% from room temperature to 1400°C. The present results shine a light on Lu₄Si₂O₇N₂ as a promising target GB phase for the optimization of high-temperature mechanical properties of Si₃N₄.

Low-temperature cofired ceramic (LTCC) is a multilayer 3D packaging, interconnection, and integration technology. For LTCC modules targeting radio and microwave frequency (RF and MW) applications, a low or near 0 ppm/°C temperature coefficient of resonant frequency (τ_f) ensures temperature stability of embedded resonator and filter functions. The base dielectrics of most commercial LTCC systems have a τ_f in the range −50 to −80 ppm/°C. This study explored a method to achieve a zero τ_f on stripline (SL) resonators by locally cofiring, in a multilayer LTCC structure, compensating dielectrics (CD) with an opposite τ_f to that of the host dielectric. The formulation, synthesis, dielectric properties, and microstructure of SrTiO₃ (STO)-based low-fire τ_f CD are presented. Chemical interactions and physical compatibility between the compensating and the host LTCC dielectrics are investigated for cofireability. The dependence of τ_f compensation on the wt% of STO, the printed thickness, and the location of the CD in multilayer LTCC are discussed. The most effective τ_f compensation is achieved by integrating CD next to the resonator lines, and can be explained by the concentration of electromagnetic energy via total internal reflection of electromagnetic waves inside the CD layer.

We investigate the high-temperature compressive deformation behavior of a novel, fully dense and structurally uniform, 20 vol% multiwalled carbon nanotube (MWCNT)–α-Al₂O₃ matrix hybrid, which has a strong room-temperature interfacial shear resistance (ISR) and a unique MWCNT-concentrated grain-boundary (GB) structure. We realized a perfect plastic deformation at 1400°C and a rather high initial strain rate of 10⁻⁴ s⁻¹ by a low ~30 MPa flow stress, which is contrary to the strain hardening response of fine-grain monolithic Al₂O₃. This unique performance in CNT–ceramic system in compression is explained as follows: the concentrated network of individual MWCNTs perfectly withstands the high-temperature and shear/compressive forces, and strongly preserves the nanostructure of Al₂O₃ matrix by preventing the dynamic grain growth, even during a large ~44% deformation. Furthermore, the presence of large amount of radially soft/elastic, highly energy-absorbing MWCNTs in the GB and specially multiple junction areas, and a potentially weak 1400°C-ISR, could greatly facilitate the GB sliding process (despite the hybrid's strong room-temperature ISR), as evidenced by the formation of some submicrometer-scale MWCNT aggregates in GB area, the equiaxed grains and dislocation-free nanostructure of the deformed hybrid. The results presented here could be attractive for the ceramic forming industry and could be regarded as a reference for oxide systems in which, the GB areas are occupied with soft/elastic, highly energy-absorbing nanostructures.

Ba₂CoNbO₆ ceramic samples were synthesized by solid-state reaction technique. X-ray photoemission spectroscopy reveals the coexistence of mixed-valent structure of Co²⁺/Co³⁺ in the sample. Dielectric measurements reveal that the sample shows colossal dielectric behavior. This behavior is contributed by two thermally activated dielectric relaxations: the low-temperature relaxation is a polaron relaxation resulting from the hopping motions of self-trapped holes; the high-temperature relaxation is a Maxwell–Wagner relaxation caused by the grain-boundary response. Our results indicate a multirelaxation mechanism, i.e., the coupling of the polaronic relaxation and the Maxwell–Wagner relaxations might be a common origin of the colossal dielectric behavior found in different materials.

CaSi₂O₂N₂: Eu²⁺ phosphors with zinc acetate additive as a flux agent have been synthesized successfully by solid-state process. The structure, morphology, and photoluminescence (PL) properties of the compounds are investigated as a function of zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) dosage. X-ray diffraction (XRD) measurement indicates that the pure CaSi₂O₂N₂ phase is obtained by adding appropriate amount of zinc acetate dehydrate. The sheetlike morphology of sample transforms into block as Zn(CH₃COO)₂·2H₂O content reaching 43 wt%, associated with the increase in emission intensity. A strong absorption band from near ultraviolet (NUV) to visible range and a broad yellow emission band in the wavelength range of 460–700 nm are observed in Eu²⁺-doped CaSi₂O₂N₂. High bright yellowish light emitting diodes are obtained by combining CaSi₂O₂N₂:Eu²⁺ as the wavelength conversion phosphor with NUV InGaN LED-chip (395 nm). The bright yellowish emission and the low thermal quenching effect of CaSi₂O₂N₂: Eu²⁺ with zinc acetate additive make it a potential phosphor converter for white LEDs.

The effect of Lu surface concentration on oxygen permeation in polycrystalline α-alumina wafers was determined at 1773 K under limited oxygen potential gradients (Δ), where the two surfaces of the wafer were deliberately subjected to different oxygen partial pressures [ (I) ≪  (II)]. When oxygen permeation occurred mainly by oxygen GB diffusion under a Δ generated by a combination of low values, the Lu-coating on the (I) [ (II)] surface decreased [increased] the oxygen permeability constants. When Δ was the result of a combination of high values, where oxygen permeation proceeded mainly by aluminum GB diffusion, the oxygen permeability constants were decreased only by the Lu-coating on the (I) surface. The analysis of mass transfer parameters, such as the chemical potentials, GB diffusion coefficients, and fluxes of aluminum and oxygen in the wafers, suggested that ambient oxygen molecules were effectively attracted toward Lu-coated surfaces exposed to low- environments, leading to a change in oxygen permeability.

The possibility of developing large solid oxide fuel cell (SOFC) stacks based upon 25 cm² ceramic oxide anode-supported cells is investigated. Planar fuel cells comprising strontium titanate-based anode support impregnated with active catalysts were prepared using a combination of deposition techniques. The fuel cell tests performed in a semisealed rig have shown power densities of 185 mW cm⁻² at 850°C using humidified hydrogen as fuel and air as oxidant. The structure and evolution of the catalytically active impregnated materials-10 mol% Gd-doped CeO₂ and nickel- are analysed using electron microscopy at the end of the fuel cell test, revealing that a ceria and nickel layer surrounds the titanate backbone grains while ~50–150 nm spherical-like nickel particles uniformly decorate this top layer.

K₃Gd(PO₄)₂:RE³⁺ (RE = Eu, Tb) are prepared by solid-state reaction and their photoluminescence (PL) properties are investigated under UV and VUV excitation, respectively. The obtained experimental data show that no energy transfer happens among the activator ions Tb³⁺ or Eu³⁺ under UV excitation. Under 147-nm excitation, the strongest emission intensity of K₃Gd(PO₄)₂:RE³⁺ (RE = Eu, Tb) is obtained when the activator ions Tb³⁺ or Eu³⁺ concentration is 0.8 mol, the integrate emission intensity of K₃Gd_0.2(PO₄)₂:0.8Tb³⁺ is about 204% of commercial phosphor Zn_1.96SiO₄:0.04Mn²⁺ with chromaticity coordinates of (0.340, 0.561) and the decay time of about 5.09 ms under 147-nm excitation. We analyze the experimental data and propose a possible energy-transfer mechanism under 147-nm excitation.

Structural and dielectric properties of (1−x)BaTiO₃–xBi(Mg_1/2Ti_1/2)O₃ (x = 0.1–0.5) were investigated to understand the binary system and utilize it for high-voltage, high energy density capacitors. The solubility limit for Bi(Mg_1/2Ti_1/2)O₃ in a BaTiO₃ perovskite was between x = 0.4 and x = 0.5. A phase with pseudocubic symmetry was formed for x = 0.1–0.4; a secondary phase developed at x = 0.5. Dielectric measurements showed highly diffusive and dispersive relaxor-like characteristics from 10 to 40 mol% of Bi(Mg_1/2Ti_1/2)O₃. These compositions also showed high relative permittivity with low-temperature coefficients of permittivity over a wide range of temperatures −100°C–600°C. Relaxation behavior was quantitatively investigated using the Vogel–Fulcher model, which revealed the activation energy of 0.17–0.22 eV. Prototyped multilayer capacitors of 18 mm × 17 mm × 4 mm dimensions with a capacitance of 12.5 nF at 1 kHz were successfully constructed and demonstrated multiple charge–discharge characteristics up to 10 kV.

The 0.72Bi(Fe_1−xAl_x)O₃–0.28BaTiO₃ (x = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx–BT) lead-free high-temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high-temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx–BT ceramics evolve from rhombohedral structure with x < 0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x ≈ 0.01, finally to pseudocubic phases when x > 0.03. Remarkably high-temperature stability with near-zero temperature coefficient of piezoelectric properties (TCk_p), together with improved piezoelectric properties has been achieved for x = 0.01 BFAx–BT ceramics. The BFAx–BT(x = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d₃₃ = 151 pC/N, k_p = 0.31 and super-high-temperature stability of T_d = 420°C, TCk_p = 1 × 10⁻⁴. It is considered that the observed strong piezoelectricity and remarkably high-temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk_p value and the pseudocubic phases possess a negative TCk_p value. Thus, the TCk_p value of BFAx–BT ceramics can be tuned by composition of x.

Owing to the widespread presence of electromagnetic interferences, it is necessary to develop new materials with excellent high-temperature electromagnetic wave (EM) absorption properties. In the present work, ZnO is infiltrated into porous ZrSiO₄ substrates to form ZnO/ZrSiO₄ composite ceramics using sol-gel process. The doping of aluminum results in the improvement of electrical conductivity and the significant change in the morphology of ZnO. With the increase in environment temperature during measurement, the permittivity of the composite ceramics increases first and then decreases dramatically, which is attributed to the change in conductive loss. The electrical conductivity increases with increasing measurement temperature. However, the concentration of oxygen vacancies decreases under air atmosphere when the measurement temperature increases continuously, which results in the reduction in conductivity. Therefore, permittivities of the undoped and doped ceramics measured at 673 K are higher than the ones at the other temperatures. The composite ceramics maintain a relatively high EM absorption coefficient, low reflection coefficient (RC), and wide effective absorption bandwidth at environment temperatures up to 773 K. As a result, we conclude that the ZnO/ZrSiO₄ composite ceramics exhibit a promising prospect as a kind of high-temperature EM absorbing material.

Nanoparticles of Co_0.6Zn_0.4Fe₂O₄, with narrow size distribution, regular morphology, and high saturation magnetization, have been synthesized. The synthesis, involved a very rapid mixing of reducible metal cations with sodium borohydride, is carried out in a colloid mill and followed by a separate hydrothermal process. The microstructure and magnetic properties of the synthesized nanoparticles are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The effects of different synthesis conditions (synthesis temperature and reaction time) on the characteristics of the ferrite nanoparticles are discussed. The changes in cation contribution are revealed by the Raman study. The magnetic measurements explore that all the as-synthesized samples are superparamagnetic in nature. The corresponding superparamagnetic behavior is explained by paramagnetic Langevin theory. Note that, the superparamagnetic Co_0.6Zn_0.4Fe₂O₄ ferrite nanoparticle, with excellent performance, can be synthesized at 160°C for a short reaction time (4 h).

A new sample of triple oxides—barium–thulium bismuthate Ba₂TmBiO₆ with perovskite structure—has been synthesized by ceramic technology. The unit cell parameters of the sample and the coefficients of thermal expansion have been determined by the method of X-ray analysis. Thermal properties of the sample have been studied by DTA over the temperature range of 293–1473 K. The heat capacity of the compound has been measured over the range of 5–320 K by vacuum adiabatic calorimetry. Thermodynamic functions of the compound have been determined based on the heat capacity data.

A graphene-supported Ce–SnS₂ (Ce–SnS₂/graphene) nanocomposite has been synthesized via a hydrothermal route. Structure, morphology, and electrochemical properties of the composites were studied by means of XRD, SEM, TEM, Raman, XPS, TGA, and electrochemical measurements. The Ce–SnS₂ crystal particles with a flower-like structure were distributed on the graphene sheets (GNS). The particle sizes of each petal are in the range 50–100 nm with clear lattice fringes. The atomic ratio of Sn, S, Ce, C, and O is estimated to be 1:2:0.05:3.11:0.64 and the content of Ce–SnS₂ composite is 80 wt.% in the as-synthesized sample. The Ce–SnS₂/graphene composite exhibits high initial discharge capacity (1638.3 mAh/g at 0.5 C), high capacity retention (707 mAh/g at 0.5 C after 50 cycles), and good rate capability due to the synergy effect between Ce–SnS₂ nanoparticles and graphene nanosheets. The superior performance is ascribed to the presence of graphene keeping the structure stable.

The pristine layered cuprate Pr₂CuO₄ samples of >95% density were fabricated as thin disks. The samples, analyzed by X-ray diffraction and Scanning electron microscopy, showed clean T′-type phase with Rietveld refined lattice parameters a = b = 3.95805(±5) Å and c = 12.2262(±5) Å. The measured dielectric properties of the Pr₂CuO₄ ceramics, in the temperature range −100°C–150°C and frequencies (ν) 0.1 Hz–1 MHz, showed extremely high ε_r′ > 10⁴ (above −30°C), and dissipation (tan δ = ε_r′′/ε_r′) between 0.1 and 5 (for 500 Hz ≤ ν ≤ 1 MHz, and −100 ≤ T ≤ 150°C). The ac conductivity of Pr₂CuO₄ ceramics ranged between 10⁻⁶ and 10⁻³ Scm⁻¹ for the measured frequencies and temperatures, and showed frequency-dependent double power law behavior akin to a modified Jonscher's power law.

The evolution of the metastable phases in metakaolin/Ca(OH)₂ systems cured at high temperatures, remains mostly unknown, newer techniques may now help to establish both the kinetic mechanism of the pozzolanic reaction and the thermodynamic stability of the main hydrated hexagonal phases: Stratlingite (C₂ASH₈) and tetra calcium aluminate hydrate (C₄AH₁₃). For this reason this work examines the kinetics of the pozzolanic reaction in the MK/Ca(OH)₂ system over 123 d at 60°C using nuclear magnetic resonance spectroscopy (²⁷Al and ²⁹Si NMR). The results obtained by ²⁷Al and ²⁹Si NMR show that during the first 30 h, the metastable phases C₂ASH₈ and C₄AH₁₃, coexist with the cubic phase (C₃ASH₆) obtained directly from the pozzolanic reaction. The gel C–S–H is clearly identified after 21 h of reaction, whereas at shorter times the C–S–H bands overlap those with the unreacted metakaolin ones. After 123 d of pozzolanic reaction, the first signs of the cubic phase are detected, a consequence of the conversion reaction of the metastable phases, and a phenomenon not previously identified.

Using a sol-gel method Pb_0.8Ba_0.2ZrO₃ (PBZ) thin film with a thickness of ~320 nm was fabricated on Pt(111)/TiO_x/SiO₂/Si substrate. The analysis results of XRD, SEM, and dielectric properties revealed that this thin film is a (111)-oriented nano-scaled antiferroelectric and ferroelectric two-phase coexisted relaxor. Calculations of dielectric tunability (η) and figure-of-merit (FOM) at room temperature display a maximum value of 75% at E = 560 kV/cm and ~236, respectively. High-temperature stability (η > 75% and FOM > 230 at 560 kV/cm in the range from 300 to 380 K) and high breakdown dielectric strength (leakage current < 1 nA at 598 kV/cm) make the PBZ thin film to be an attractive material for applications of tunable devices.

A pressure-induced phase transformation is used to refine the grain size of polycrystalline Y₂O₃, by a factor of 3000. A surface modification effect accompanies the observed grain refinement, which becomes more apparent with increasing holding time under high pressure. The surface-modified layer exhibits lower hardness and lower oxygen content relative to the underlying material. Moreover, it possesses columnar-grained structure with cubic symmetry, whereas the interior has a monoclinic structure.

A ZnO varistors in series connected with a semi-insulating GaAs photoconductive switches (SI-GaAs PCSS's), a test method for ultrafast pulse response characteristics of ZnO varistor ceramics with DC bias was presented for the first time. The DC voltage distribution of the PCSS's and the varistors was measured in a dark state and the pulse response characteristics of the ZnO varistor ceramics was examined by a nanosecond laser pulse illuminating the PCSS's. The results indicate that the electric pulse output from the varistors includes capacitive current and conduction current and there is a time delay between their peaks. It is revealed that ZnO varistors has a nonlinear conductivity for the nanosecond electric impulse excitation and the barrier capacitance decay constant of the ceramics sample is 105 ns, which is explained through the analysis of examining the material structure and the conductive mechanisms.

Bulk ceramic 72.5 mol%(Bi_0.5Na_0.5)TiO₃–22.5 mol%(Bi_0.5K_0.5)TiO₃–5 mol%Bi(Mg_0.5Ti_0.5)O₃ (BNT–BKT–BMgT) has previously been reported to show a large high-field piezoelectric coefficient (d₃₃* = 570 pm/V). In this work, the same composition was synthesized in thin film embodiments on platinized silicon substrates via chemical solution deposition. Overdoping of volatile cations in the precursor solutions was necessary to achieve phase-pure perovskite. An annealing temperature of 700°C resulted in good ferroelectric properties (P_max = 52 μC/cm² and P_r = 12 μC/cm²). Quantitative compositional analysis of films annealed at 650°C and 700°C indicated that near ideal atomic ratios were achieved. Compositional fluctuations observed through the film thickness were in good agreement with the existence of voids formed between successive spin-cast layers, as observed with electron microscopy. Bipolar and unipolar strain measurements were performed via double laser beam interferometry and a high effective piezoelectric coefficient (d_33,f) of approximately 75 pm/V was obtained.

The ceramic precursor for HfB₂/HfC/SiC/C was prepared via solution-based processing of polyhafnoxanesal, linear phenolic resin, boric acid and poly[(methylsilylene)acetylene)]. The obtained precursor could be cured at 250°C and subsequently heat treated at relative lower temperature (1500°C) to form HfB₂/HfC/SiC/C ceramic powders. The ceramic powders were characterized by element analysis, thermal gravimetric analysis, X-ray diffraction, Raman spectroscopy, and Scanning electron microscopy. The results indicated that the ceramic powders with particle size of 200~500 nm were consisted of pure phase HfB₂, HfC, and SiC along with free carbon as fourth phase with low crystallinity.

The resistance of EB-PVD Gd₂Zr₂O₇ thermal barrier coatings against high-temperature infiltration and subsequent degradation by molten volcanic ash is investigated by microstructural analysis. At 1200°C, EB-PVD Gd₂Zr₂O₇ coatings with silica-rich, artificial volcanic ash (AVA) overlay show a highly dynamic and complex recession scenario. Gd₂O₃ is leached out from Gd₂Zr₂O₇ by AVA and rapidly crystallizes as an oxyapatite-type solid-solution (Ca,Gd)₂(Gd,Zr)₈(Si,Al)₆O₂₆. The second product of Gd₂Zr₂O₇ decomposition is Gd₂O₃ fully stabilized ZrO₂ (Gd-FSZ). Both reaction products are forming an interpenetrating network filling open coating porosity. However, first-generation Gd-oxyapatite and Gd-FSZ are exhibiting chemical evolution in the long term. The chemical composition of Gd-oxyapatite does evolve from Ca,Zr enriched to Gd-rich. AVA continuously leaches out Gd₂O₃ from Gd-FSZ followed by destabilization to the monoclinic ZrO₂ polymorph. Finally, zircon (ZrSiO₄) is formed. In addition to the prevalent formation of Gd-oxyapatite, a Gd-, Zr-, Fe-, and Ti-rich oxide is observed. From chemical analysis and electron diffraction it is concluded that this phase belongs to the zirconolite-type family (zirconolite CaZrTi₂O₇), exhibiting an almost full substitution Ca²⁺ + Ti⁴⁺ <> Gd³⁺ + Fe³⁺. As all Gd₂Zr₂O₇ decomposition products with the exception of ZrSiO₄ exhibit considerable solid solubility ranges, it is difficult to conclusively assess the resistance of EB-PVD Gd₂Zr₂O₇ coatings versus volcanic ash attack.

Dielectric and impedance spectroscopies were employed to study the electrical behavior of (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (abbr. BCTZ) lead-free ceramic. The dielectric properties versus dc bias electric field experiment revealed high dielectric tunability (> 65%) as well as figure of merit (> 27) at 10 kHz and room temperature. At elevated temperature range, a dielectric loss peak was observed and verified to be correlate of oxygen vacancy relaxation. The impedance spectra studies indicate that the ceramic is a mixed ionic conductor of p-type nature at the paraelectric phase and, the grain and total conductivity at 600°C reaches 6.0 × 10⁻⁵ and 2.0 × 10⁻⁵ S/cm, respectively.

The controllable formation of zinc oxide (ZnO) nanostructures and nanowires by a cheap and environmental friendly fabrication method of simply subjecting metallic zinc films in sodium chloride (NaCl) solution at 170°C from 3 to 15 h under hydrothermal conditions is demonstrated in this study. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate that ZnO films with different morphologies are obtained: from a film with network of circular pores to a film with nanowire-like network with bigger pores. It is observed that heating duration has an effect on its photoluminescence (PL) properties. Ultraviolet emission is observed for all ZnO films. Green emission surfaces after heating for 6 h, which subsequently disappears after 15 h of heating. It is suggested that the morphology change over different heating durations is responsible for the rise and subsequent decline in green emissions. Lastly, the growth mechanism behind zinc oxidation and morphology change is proposed and investigated with the aid of experimental method. It is verified that pitting corrosion is responsible for the growth mechanism here.

The effect of the activator concentration on the structure of alkali silicate-activated slag/metakaolin pastes is assessed through synchrotron radiation-based X-ray techniques. As main reaction products, both calcium aluminosilicate hydrate (C–A–S–H) and sodium/calcium aluminosilicate hydrate [(C,N)–A–S–H] type gels are formed in activated binders solely based on slag, along with the zeolitic products gismondine and garronite. In activated blended pastes, the inclusion of metakaolin in the binder hinders the formation of zeolite products, instead favoring the formation of a (C,N)–A–S–H type gel consistent with the activation of metakaolin in the presence of high concentrations of Ca. The formation of the two distinct binding products is confirmed by high-resolution X-ray fluorescence microscopy, where the “inner” products and the “outer” products have compositions consistent with (C,N)–A–S–H and C–A–S–H type gels, respectively. These results provide important new insights into the gel chemistry and micro/nanostructure of blended alkali-activated binder systems.

Finely ground mineral powders are known to accelerate cement hydration rates. This “filler effect” has been attributed to the effects of dilution (w/c increase) when the cement content is reduced or to the provision of additional surface area by fine powders. The latter contribution (i.e., surface area increase) is speculated to provide additional sites for the nucleation of the hydration products, which accelerates reactions. Through extensive experimentation and simulation this study describes the influence of surface area and mineral type (e.g., quartz or limestone) on cement reaction rates. Simulations using a boundary nucleation and growth (BNG) model and a multiphase reaction ensemble (MRE) indicate that the extent of the acceleration is linked to the: (1) magnitude of surface area increase and (2a) capacity of the filler's surface to offer favorable nucleation sites for hydration products. Other simulations using a kinetic cellular automaton model (HydratiCA) suggest that accelerations are linked to: (2b) the interfacial properties of the filler that alters (increases or decreases) its tendency to serve as a nucleant, and (3) the chemical composition of the filler and the tendency for its dissociated ions to participate in exchange reactions with the calcium silicate hydrate product. The simulations are correlated with accelerations observed using isothermal calorimetry when fillers partially replace cement. The research correlates and unifies the fundamental parameters that drive the filler effect and provides a mechanistic understanding of the influence of filler agents on cementitious reaction rates.

As the oxidation and chromium volatilization of chromia-forming alloy interconnects can cause Solid oxide fuel cells (SOFC) cathode poisoning and cell degradation, spinel coatings like Mn_1.5Co_1.5O₄ have been applied as a barrier to oxygen and chromium diffusion. To evaluate their long-term stability, the properties of the reaction layer between the Mn_1.5Co_1.5O₄ coating and Cr₂O₃ scale formed on the alloy surface need to be characterized. Therefore, compositions of Mn_1.5−0.5xCo_1.5−0.5xCr_xO₄ (x = 0–2) were prepared to investigate their electrical properties, cation distributions, and thermal expansion behavior at high temperature. With increasing Cr content in manganese cobalt spinel oxides, the cubic crystal structure is stabilized and the electrical conductivity and coefficient of thermal expansion both decrease. The cation distributions determined from neutron diffraction show that Cr and Mn have stronger preference for octahedral sites in the spinel structure as compared with Co.

Using the solid-state reaction method, Ce³⁺,Tb³⁺-coactivated Si₅AlON₇ (Si_6−zAl_zO_zN_8−z, z = 1) phosphors were successfully synthesized. The obtained phosphors exhibit high absorption and strong excitation bands in the wavelength range of 240–440 nm, matching well with the light emitting-diode (LED) chip. The ET from Ce³⁺ to Tb³⁺ ions in Si₅AlON₇:Ce³⁺,Tb³⁺ has been studied and demonstrated by the luminescence spectra and decay curves. Moreover, the phosphors show tunable emissions from blue to green by tuning the relative ratio of the Ce³⁺ to Tb³⁺ ions. Thermal quenching properties of Si₅AlON₇:Ce³⁺,Tb³⁺ had also been investigated and the quenching temperature is ~190°C. These results show that Si₅AlON₇:Ce³⁺,Tb³⁺ could be a promising candidate for a single-phased color-tunable phosphor applied in UV-chip pumped LEDs.

Structural, elastic, optical, thermodynamical, and electronic properties of yttrium oxide compound in cubic phase have been studied using the full-potential augmented plane waves (FP-LAPW) within density functional theory (DFT) framework. Four different approximations were used for exchange-correlation potentials terms, comprised Perdew–Burke–Ernzerhof generalized parameterization of gradient approximation (GGA-PBE), Wu–Cohen (WC-GGA), local-density approximation (LDA), and new approximation modified Becke and Johnson (mBJ-GGA). The structural properties such as equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Moreover, Elastic constants, Young's modulus, shear modulus, Poisson's ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature, and Grüneisen parameters have been calculated. Obtained structural, elastic and other parameters are consistent with experimental data. Moreover pressure dependence of the elastic moduli was studied. From electronic calculations, it has been found that the band gap was 5.7 eV at Г point in the Brillouin zone using mBJ-GGA approximation. Optical properties, such as the dielectric function, refractive index, extinction index, and optical band gap, were calculated for radiation up to 14 eV. In addition, the unique type of bonding in Y₂O₃ was discussed by three method including effective charge, B/G ratio, and charge density distribution.

This study presents the results of atomic force microscopy (AFM)-localized impedance measurements within Si₃N₄/glassy phase/TiC heterogeneous nanostructures. The three phases show significant differences in the charge-transfer resistance and interface capacitance values detected on the plasma-etching surface by an ultrasharp AFM, and these characteristics are helpful to understand the sintering behavior in spark plasma sintering. The effect of an electrical field may induce localized Joule heating on conductive nano-TiC embedded in the Si₃N₄-based matrix. The glassy phase doped with Ti and C, as observed by transmission electron microscopy, may promote electrowetting, leading to enhanced densification in the insulating/conductive ceramic nanocomposite system.

A new thiogallate-based green-emitting phosphor, MgGa₂S₄:Eu²⁺, was first synthesized via a high-temperature solid-state reaction in a CS₂ atmosphere. We then investigated the structures and luminescent properties of the MgGa₂S₄:Eu²⁺ phosphors. The MgGa₂S₄:Eu²⁺ phosphors can be excited efficiently by UV–visible light in the wavelength range from 350 to 520 nm and they emit an intensely green light with emission bands peaking at 538 nm. The optimal concentration for Eu²⁺ in MgGa₂S₄ was found to be about 6 mol%, and the corresponding concentration quenching mechanism was the electric multipole–multipole interaction. The quenching temperature was calculated to be 402 K, and the Huang–Rhys factor was about 4. The energy barrier for thermal quenching was calculated to be 0.28 and 0.27 eV by the two types of the Arrhenius equations. The small variation in the color coordinates of MgGa₂S₄:Eu²⁺ under high temperatures indicates that the as-synthesized phosphor has good color stability. Due to their broadband absorption in the 350–520 nm wavelength range, these phosphors may be able to fulfill the requirements for application in the development of Ga(In)N-based white LEDs.

In the present work, porous lead zirconate titanate (PZT) ceramics with porosity ranging from 27.8% to 72.4% were fabricated by the gel-casting process of particle-stabilized wet foams with the initial solid loading of 10–30 vol%. The phase, the microstructure, the dielectric property, and the piezoelectric property were characterized. The relative permittivity (ε_r) and longitudinal piezoelectric strain coefficient (d₃₃) of the investigated samples decreased with increasing porosity. Both the values of hydrostatic strain coefficient (d_h) and hydrostatic voltage coefficient (g_h) increased moderately with the increase in porosity, which was beneficial for enhancing the value of hydrostatic figure of merit (HFOM). As a result, the prepared sample possessed a maximal HFOM value of 15236 × 10⁻¹⁵ Pa⁻¹ with the porosity of 72.4%. The acoustic impedance (Z) of specimens decreased linearly with increasing porosity, and had the lowest value of 1.95 MRayls, making them promising candidates for application of medical ultrasonic imaging or underwater sonar detectors.

The degradation phenomena of ZnO and SnO₂-based varistors were investigated for two different degradation methods: DC voltage at increased temperature and degradation with 8/20 μs pulsed currents (lightning type). Electrostatic force microscopy (EFM) was used to analyze the surface charge accumulated at grain-boundary regions before and after degradation. Before the degradation process, 85% of the barriers are active in the SnO₂ system, while the ZnO system presents only 30% effective barriers. Both systems showed changes in the electrical behavior when degraded with pulses. In the case of the ZnO system, the behavior after pulse degradation was essentially ohmic due to the destruction of barriers (about 99% of the interfaces are conductive). After the degradation with 8/20 μs pulsed currents, the SnO₂ system still presents nonohmic behavior with a significant decrease in the quantity of effective barriers (from 85% to 5%). However, when the degradation is accomplished with continuous current, the SnO₂ system exhibits minimum variation, while the ZnO system degrades from 30% to 5%. This result indicates the existence of metastable defects of low concentration and/or low diffusion in the SnO₂ system. High energy is necessary to degrade the barriers due to defect annihilation in the SnO₂ system.

Oxynitride long-lasting phosphorescence (LLP) phosphor SrSi₂O₂N₂:Eu²⁺ was prepared by a new method using SrSi alloy as a precursor. Its properties were systematically investigated utilizing XRD, photoluminescence, excited-state decay curve, long-lasting phosphorescence, and thermoluminescence spectrum. This phosphor was found to be well-crystallized by calcinations of the Sr_1−xEu_xSi alloy and the SiO₂ mixture at 1400°C for 3 h. After irradiation under the 280 nm UV light, the afterglow emission of Eu²⁺ (4f⁶5d¹ → 4f⁷) was obviously observed for at least 2 h in the limit of light perception of dark-adapted human eyes (0.32 mcd/m²). Furthermore, the possible mechanism for the LLP of SrSi₂O₂N₂:Eu²⁺ phosphor is also discussed in this article.

In this study, magnesium (Mg) was doped into the non-calcined amorphous calcium phosphate (ACP) via mechanochemical route, and the as-prepared non-calcined ACP was used to form a novel hydration system. In this novel hydration system, the effects of Mg doping on the hydration reaction and mechanical property of cement were studied. The incorporation of Mg into the hydration product was confirmed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results showed that Mg doping had a significant influence on the nucleation and subsequent growth of apatite crystals. With the Mg doping, the size of hydration crystals was refined, and induced a denser curing body after setting. With the increasing density, the mechanical property of cement was improved effectively. This work explored the inhibiting effect of Mg ions on the nucleation and subsequent growth of apatite under the non-calcined condition.

The disorder in γ–alon is caused by random arrangement of nitrogen atoms and aluminum vacancies. To understand the properties and electronic structure of γ–alon by theoretical methods, the most reasonable structure model is needed. We examined the site preference of nitrogen atoms and aluminum vacancies by first-principles density functional theory (DFT) calculations on Al₂₄O₂₄N₈ and Al₂₃O₂₇N₅. The calculated results for Al₂₄O₂₄N₈ with the lowest total energy indicated that nitrogen atoms prefer to be far away from each other, rather than in a completely random arrangement. The further investigation on Al₂₃O₂₇N₅ shows that the aluminum vacancies tend to possess octahedral sites and coordinate only with oxygen atoms. Evaluated by lattice variances (D_a and D_θ) and simulated XRD pattern, the most reasonable structure model of Al₂₃O₂₇N₅ has little deviation from the experimental results. The calculated bulk modulus of 200.9 GPa in Al₂₃O₂₇N₅ is slightly lower than the experimental value. The electronic structure reveals that the bonds of Al–N and Al–O have partially covalent and ionic characterization, while the covalent bond strength of Al–N is stronger than that of Al–O. The calculated band gap is 3.99 eV, which is much closer to the experimental 4.56 eV than previous suggestions.

Uniform coating of nanometer-scale BaTiO₃–Dy₂O₃–SiO₂ layers on spherical Ni particles are achieved by controlled hydrolysis of tetrabutyl titanate (TBT), hydrothermal reaction with Ba(OH)₂, and co-precipitation of tetraethylorthosilicate (TEOS) and Dy(NO₃)₃. The composition of the coating layer is similar to rare earth oxide-silica–doped BaTiO₃, which is the main component of dielectric layer for base metal electrode (BME) multilayer ceramic capacitors (MLCCs). After coating, the shrinkage onset temperature of Ni particles is significantly increased. After sintered to pellets, the electrode has good electrical conductivity. This electrode material has good compatibility with rare earth oxide and silica-doped BaTiO₃ dielectric materials, and could serve as promising candidate for application in the next generation BME-MLCCs.

The fabrication of 0.5 mol% Ce:LuAG transparent ceramics starting from synthetic nanosized Ce:LuAG powders was investigated by low temperature vacuum sintering. It was found that high quality optical Ce:LuAG ceramics could be densified successfully by vacuum sintering (<10^–3 pa) at 1750°C for 10 h. The in-line optical transmittance of as-sintered Ce:LuAG ceramics with thickness of 0.7 mm could reach 73.48% at the wavelength of 550 nm. The microstructure observations revealed that transparent Ce:LuAG ceramics were composed of uniform LuAG grains with average size of 9 μm and HRTEM morphology indicated that no impurity segregation existed at grain boundaries or within Ce:LuAG grains. It was also demonstrated that the annealing treatment (at 1450°C for 20 h in air) could greatly enhance the luminescent intensity of as-sintered Ce:LuAG ceramics under excitation of X-ray radiation (75 kV, 25 mA), which makes it a potential candidate to be applied in radiation detector.

β-eucryptite (LiAlSiO₄), a member of the family of lithium aluminum silicates, is known to undergo a reversible pressure-induced phase transformation at ~0.8 GPa to ε-eucryptite. This study correlates the results between two techniques, in situ diamond anvil cell–Raman spectroscopy and nanoindentation experiments, to explore how doping (substituting Zn for Li) influences this pressure-induced phase transformation. Diamond anvil cell tests carried up to 3 GPa hydrostatic stress under Raman spectroscopy were compared with nanoindentation results, which provide a more localized, multiaxial stress state. The results indicate that the magnitude of hysteresis observed (difference between the pressures required for the forward and reverse transformation) is lower for Zn-doped β-eucryptite; however, the onset of the phase transformation is unchanged by doping with Zn. Furthermore, calculations of activation volume from nanoindentation experiments yield similar values (~0.1 nm³) for pure and Zn-doped β-eucryptite, suggesting that the nucleation event that establishes the onset of the phase transformation is the same for both materials.

A new sulfated chitosan superplasticizer (SCS) was synthesized by sulfation chitosan. The chemical structure and molecular weight of SCS were characterized by FTIR and gel permeation chromatography (GPC). The application performances of SCS in cement paste and concrete were investigated in the views of fluidity, slump, setting time, porosity as well as compressive strength. The results indicated that the SCS has better applied performance compared with polycarboxylate superplasticizer (PCs). A notable feature is that SCS has better maintenance for cement paste fluidity and concrete slump. The action mechanism behind this behavior was further revealed by zeta-potential and adsorption amount. Meanwhile, SCS comes from renewable source and has biodegradability. This research work provides not only a new superplasticizer but also a method for preparing superplasticizer from the renewable biopolymer.

Sm³⁺-doped glass 13SrO–2Bi₂O₃–5K₂O–80B₂O₃ was fabricated by the conventional melt-quenching technique. The glass-ceramics were obtained by heating the as-prepared glasses in air atmosphere at selected temperatures 550°C, 600°C, 615°C, and 650°C, respectively. The luminescence spectra of both Sm³⁺ and Sm²⁺ were detected in the ceramic heated at 650°C where crystalline phase is formed. The as-prepared glass and the ceramics heated at 550°C, 600°C, and 615°C show only the emission due to Sm³⁺. In the sample heated at 650°C in air atmosphere, however, part of Sm³⁺ ions was converted to Sm²⁺, giving rise to sharp emission lines which are characteristic of Sm²⁺ in crystalline state. It is suggested that Sm²⁺ ions are located at Sr²⁺ site in the ceramic while Sm³⁺ ions are located at Bi³⁺ sites. The Sm²⁺-doped glass-ceramic has a high optical stability because the fluorescence intensity decreases by only about 8% of its initial value upon excitation at 488 nm Ar⁺ laser.

We show that water-based porosimetry (WBP), a facile, simple, and nondestructive porosimetry technique, accurately evaluates both the pore size distribution and throat size distribution of sacrificially templated macroporous alumina. The pore size distribution and throat size distribution derived from the WBP evaluation in uptake (imbibition) and release (drainage) mode, respectively, were corroborated by mercury porosimetry and X-ray micro-computed tomography (μ-CT). In contrast with mercury porosimetry, the WBP also provided information on the presence of “dead-end pores” in the macroporous alumina.

A catalytic combustion-type gas sensor using a positive temperature coefficient (PTC) thermistor, which shows a sharp resistance change around Curie temperature, was developed for the detection of hydrogen. La-doped BaTiO₃ (Ba_0.998 La_0.002 TiO₃) was prepared through a solid-state method and an oxalic acid method. La-doped BaTiO₃ obtained by the oxalic acid method showed improved PTC properties, due to the formation of fine particles, as compared to that prepared with the solid-state method. The resulting sensor device showed a fairly high H₂ sensitivity in the range of 100–1000 ppm. In addition, the H₂ sensitivity and response speed were improved by coating a Pt/SiO₂ catalyst on the sensor device because the catalytic combustion efficiency of H₂ was improved by the catalyst coating.

The following article from Journal of the American Ceramic Society, “Use of Ti-Bearing Blast Furnace Slag for Fabrication of Multi-Doped Aluminum Titanate Composites with Good Thermal Stability” by Huihong Lü, Minhong Li, Xingrong Wu, and Liaosha Li, published online on 13 February 2012 in Wiley Online Library (wileyonlinelibrary.com), DOI: 10.1111/j.1551-2916.2012.05087.x, has been retracted by agreement between the authors, the journal Editor in Chief, David Green, and Wiley Periodicals, Inc.

The laser-induced crystallization method was applied to pattern β-BaB₂O₄ crystals (β-BBO) in the inside of bulk glass plate and fibers of 8Sm₂O₃–42BaO–50B₂O₃, in which the focal position of continuous wave (CW) Yb:YVO₄ fiber lasers (power: 0.9–1.0 W, scanning speed: 2 μm/s) with a wavelength of 1080 nm was moved gradually from the surface to the inside. It was confirmed from micro-Raman scattering spectra, second harmonic generation, and transmission electron microscope observations that β-BBO crystals are patterned in the inside of glass plate and fibers (diameter: 110 μm) and are highly oriented that is c-axis orientation, along the laser scanning direction. This study proposes the direct and simple processing for the fabrication of glass fibers consisting of optical functional crystal cores.

Using the flash sintering technique, cubic yttria-stabilized zirconia is shown to sinter at 390°C, more than 1000°C below nominal sintering temperatures, by using a DC electric field of 2250 V/cm. Furthermore, flash sintering experiments performed with electric fields between 60 and 2250 V/cm were used to show that the relationship of the temperature at the onset of flash sintering (T_Onset) and the applied field (E) follows the power relationship T_Onset (K) = 2440 E^−1/5.85(V/cm). Using this relationship, and considering the sintering of the sample in the absence of an electric field, the critical electric field to enter the flash sintering regime is shown to be 24.5 V/cm. For electric fields between this critical electric field and 2250 V/cm, the onset of flash sintering occurs in the same range of critical volumetric power dissipation, between 1 and 10 mW/mm³, suggesting this is a material property. Despite the volumetric power dissipation being the critical value for the onset of flash sintering behavior, the current density achieved during sintering appears to be more critical for densification rather than maximizing power dissipation.

Well-crystallized pure BiFeO₃ nanopowders were successfully synthesized at the temperature as low as 120°C by an ethanol-assisted hydrothermal process. In this synthesis, the composition of the solvent played important roles in the formation of pure BiFeO₃. The BiFeO₃ nanopowders synthesized with 4:3 ethanol/water ratio mainly consists of cubic structures with size from 50 to 150 nm. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements indicated that pure BiFeO₃ nanopowders showed a spin-glass transition below the freezing temperature. Moreover, the BiFeO₃ nanopowders exhibited ferromagnetic order at room temperature.

Near-infrared (NIR) quantum cutting involving the emission of two NIR photons for each visible photon absorbed is realized from Eu²⁺/Yb³⁺ codoped chalcohalide glasses. Excitation, emission and decay spectra are measured to prove the occurrence of cooperative energy transfer (ET) from Eu²⁺ to Yb³⁺. The maximum ET efficiency obtained is as high as 85%. The ET from Eu²⁺ to Yb³⁺ is followed by dipole-dipole interaction. The possible mechanism of ET is discussed.

We show that multilayer green tapes constituted from sandwiched layers of NiO–zirconia anode and cubic zirconia electrolyte can be sintered below 1000°C in a few seconds under the influence of a DC electric field. The sintering yields a dense electrolyte layer with minor closed porosity, and an anode layer with open porosity, and, most importantly, a multilayer that is largely devoid of defects and delamination.

Nanoscale ferroelectric honeycombs, comprised of vertically aligned PbTiO₃ nanotubes, are fabricated by vapor phase reaction between lead acetate-infiltrated TiO₂ nanotubes and PbO vapor. PbTiO₃ nanohoneycombs converted by vapor phase reaction at 550°C showed well-aligned nanoscale structure with alignment angle less than 1° and well-defined ferroelectric properties with the effective piezoelectric coefficient of 44 pm/V. This novel nanoscale structure is expected to facilitate high efficiency sensing of electromechanical and electrochemical stimuli.

MAX phase Ti₂Al_(1−x)Sn_xC solid solution with x = 0, 0.32, 0.57, 0.82, and 1 was synthesized by pressureless sintering of uniaxially pressed Ti, Al, Sn, and TiC powder mixtures. Annealing in air atmosphere at 200°C–1000°C triggered a sequence of oxidation reactions which reveal a distinct influence of solid solution composition on the oxidation process. With decreasing Al/Sn ratio, the characteristic temperature of accelerated oxidation reaction of A-element was reduced from 900°C (x = 0) to 460°C (x = 1). SnO₂ was formed at temperatures significantly lower than TiO₂ (rutile) and Al₂O₃. Substitution of A-element in MAX phase solid solution by low-melting elements such as Sn may offer potential for reducing oxidation-induced crack healing temperatures.

The complex impedance spectra of polymer-derived amorphous silicon oxycarbides synthesized at different temperatures are reported. Analysis of the spectra using equivalent circuit models showed that the conduction of current is dominantly through the matrix and free carbon in series, instead of through the matrix or free carbon only. We found that the conductivity of both matrix and free-carbon phase increases with increasing synthesis temperature, whereas the relaxation time of the matrix is much shorter than that of the free carbon. The results are correlated with the structures of the materials.

This work determines the self-diffusion coefficients of indium in TiO₂ single crystal (rutile). Diffusion concentration profiles were imposed by deposition of a thin surface layer of InCl₃ on the TiO₂ single crystal and subsequent annealing in the temperature range 1073–1573 K. The diffusion-induced concentration profiles of indium as a function of depth were determined using secondary ion mass spectrometry (SIMS). These diffusion profiles were used to calculate the self-diffusion coefficients of indium in the polycrystalline In₂TiO₅ surface layer and the TiO₂ single crystal. The temperature dependence of the respective diffusion coefficients, in the range 1073–1573 K, can be expressed by the following formulas:

and

The obtained activation energy for bulk diffusion of indium in rutile (316 kJ/mol) is similar to that of zirconium in rutile (325 kJ/mol). The determined diffusion data can be used in selection of optimal processing conditions for TiO₂–In₂O₃ solid solutions.

The control of the rheological behavior of highly loaded ceramic/polymer suspensions affords the development of near-net shape forming techniques. In this study, suspensions containing sub-micrometer diameter alumina (up to 56 vol%) were fabricated using an anionic dispersant (≈4 vol%) and water-soluble polyvinylpyrrolidone (PVP). The amount and ratio of molecular weights of PVP in the suspension were varied to influence flow behavior. The final pH of the system, ≈9.5, was higher than the isoelectric point (IEP) of alumina implying that the alumina powder possesses a negative surface charge. In the case of alumina at this pH, PVP does not adsorb onto the surface of the powder. The flow behavior of the PVP-containing suspensions displayed yield-pseudoplastic characteristics that closely agreed with the Herschel–Bulkley fluid model. The addition of PVP significantly changed the rheology of the system, increasing the shear yield stress and altering flow behavior. Interparticle interaction approximations of the suspensions were modeled to correlate with experimental observations.

Spherical granules of aluminum nitride (AlN) with an average particle size of about 50 μm were produced from aqueous suspensions using an AlN powder surface treated against hydrolysis with aluminum dihydrogenphosphate [Al(H₂PO₄)₃]. Two different amounts of Al(H₂PO₄)₃ were tested and the effects of surface treatment and aging time were evaluated by various techniques (XRD, TG-DTA, zeta potential and pH measurements). The treated powder exhibited antihydrolytic property and good dispersing behavior, enabling the preparation of low-viscosity and high-concentration aqueous AlN slurries for freeze granulation. The spherical AlN granules were sintered in a boron nitride (BN) powder bed followed by ultrasonic washing of the AlN granulates/BN mixture to remove BN. The sintered spherical AlN granules present excellent crystallinity and high sphericity as observed from SEM micrographs.

[0001] textured alumina ceramics with a fine grain size were fabricated between 1400°C and 1600°C via templated grain growth (TGG) using fine alumina platelets (~0.6 and ~3 μm diameter) aligned by tape casting in either a 50 nm α-Al₂O₃ matrix powder, or in a seeded boehmite sol. The 3 μm templates could be readily aligned by tape casting in both matrices (orientation parameters r = 0.27 and 0.18, respectively), whereas 0.6 μm diameter templates were well aligned in the seeded boehmite sol only (r = 0.29). Improved alignment in boehmite sols is attributed to inorganic gelation, resulting in a strongly pseudo-plastic rheology that preserves template alignment against the influence of Brownian motion. The in situ formation of fine α-Al₂O₃ matrix after transformation in the seeded boehmite system results in a higher driving force for TGG and improves texture development. The combination of 3 μm templates with a seeded boehmite matrix results in extremely high texture qualities (texture fraction f = 0.97–0.99, r = 0.17) while maintaining a relatively fine grain size (5–10 μm in diameter and 1.5–3 μm in thickness). Although undoped samples can be fully textured at 1600°C, adding as little as ~0.25 wt% CaO/SiO₂ dopant improves TGG kinetics and yields full texture at 1400°C.

Electro-sintering, i.e., electrically enhanced densification without the assistance of Joule heating, has been observed in 70% dense 8 mol% Y₂O₃-stabilized ZrO₂ ceramics at temperatures well below those for conventional sintering. Remarkably, full density can be obtained without grain growth under a wide range of conditions, including those standard for solid oxide fuel cell (SOFS) and solid oxide electrolysis cell (SOEC), such as 840°C with 0.15 A/cm². Microstructure evidence and scaling analysis suggest that electro-sintering is aided by electro-migration of pores, made possible by surface flow of cations across the pore meeting lattice/grain-boundary counter flow of O²⁻. This allows pore removal from the anode/air interface and densification at unprecedentedly low temperatures. Shrinkage cracking caused by electro-sintering of residual pores is envisioned as a potential damage mechanism in SOFC/SOEC 8YSZ membranes.

Highly porous ceramic foams can be produced by combining particle stabilized foams and gelcasting concepts. Sulfonate-type surfactants are selected to weakly hydrophobize the alumina surface and stabilize air bubbles in suspensions containing gelcasting additives, polyvinyl alcohol (PVA), and 2,5-dimethoxy-2,5-dihydrofurane (DHF). The aim of this work was to prepare large complex-shaped ceramic foam objects with homogeneous microstructure and high porosity. A key to avoiding drying cracks is to strengthen the wet green body via gelcasting. The influence of the amount of gelcasting additives on the mechanical strength of the ceramic foam green bodies is investigated as well as the effect of using cross-linking agent versus the addition of just a binder. The presence of a cross-linked polymeric network within the green body increases its mechanical strength and minimizes crack formation during drying.

One of the most common ways used to produce multilayer ceramics (MLC) is tape casting. In this process, the dried tape thickness is of great interest to control the desired products and applications. One of the parameters that influences the final tape thickness is the side flow factor (α) which is mostly measured at the end of the process by a volumetric comparison of the tape which flowed outside the casting width to the tape within the casting width. This phenomenon has not been predicted theoretically yet in the literature. In this study, the flow of (La_0.85Sr_0.15)_0.9MnO₃ (LSM) slurry in the tape casting process is modeled numerically with ANSYS FLUENT in combination with an Ostwald-de Waele power law constitutive equation. Based on rheometer experiments, the constants in the Ostwald-de Waele power law are identified for the considered LSM material and applied in the numerical modeling. This model is then used for different values of substrate velocity, initial doctor blade height and material load in the reservoir, to investigate their effect on α. It is found that this factor mostly ranges between 0.8 and 0.9. Results of the modeling are compared with experimental findings and good agreement is found.

Well-dispersed hollow TiO₂ spheres were synthesized via Ostwald ripening through a fluorine-free solvothermal process in a n-PrOH/H₂O mixed solvent. Several commonly used acids, such as HNO₃, HCl, and H₂SO₄, were found to be effective as the ripening-directing agent to replace the highly corrosive HF, and the hollow TiO₂ sphere size could be modulated by varying the reactant concentrations. The effects of the solvents and reactants were explored in details, which demonstrated that four important criteria existed in this fluorine-free process to create well-dispersed hollow TiO₂ spheres, including the utilization of n-PrOH/H₂O mixed solvent, certain degree of acidity, coexistence of different acids, and the existence of SO₄²⁻ in the reaction solution. After calcination for a better crystallization, these hollow TiO₂ spheres were composed of pure anatase phase, and had a good photocatalytic degradation performance on RhB under UV illumination.

This study, composed of three parts, aims at studying the crystallization behaviors of PbSe quantum dots (QDs) in silicate host glasses. Firstly, due to the importance of the choice of base glass for the QDs' crystallization, the selection of base glass compositions, the glass fragility, and glass formation ability (GFA) are discussed in details, and the results show that the selected glass compositions have an intermediate fragility and accordingly an intermediate glass transition temperature range among a wide variety of inorganic glass systems together with a good GFA/glass stability (GS). Thus, this base glass is suitable as the host glass in which PbSe QDs crystallize. Secondly, the experimental results on PbSe QDs' crystallizations are presented, and the results show that PbSe QDs can precipitate from silicate glasses favorably with no other chemical compounds precipitation, and the optimized temperature for PbSe QDs crystallization is 600°C. Lastly, the classical nucleation theory is used to analyze the PbSe QD crystallization behaviors in host glasses. The steady-state nucleation rates and the growth rates of PbSe QDs as well as the time–temperature transformation (TTT) curves are calculated. The results indicate that the free surface energy between the PbSe nuclei and the host glass has great influence on the nucleation rates of PbSe QDs, while it has less effect on the growth rates of PbSe QDs; the crystallization behaviors of PbSe QDs with different volume fractions can be described well by the TTT curves while keeping the dimensionless empirical constant, α, unchanged for one certain curve.

Revealing and understanding the microscopic origins of the macroscopic properties of aluminosilicate glasses is important for the design of new glasses with optimized properties. In this work, we study the composition-structure-property relationships in 20 MgO/CaO sodium aluminosilicate glasses upon Al₂O₃-for-SiO₂ and MgO-for-CaO substitutions. We find that some properties (density, molar volume, Young's modulus, and shear modulus) are linear through the investigated range of Al₂O₃ compositions, while others (refractive index, coefficient of thermal expansion, Vickers hardness, isokom temperatures, and liquid fragility index) exhibit a change in the slope around the composition with [Al₂O₃] = [Na₂O], which is especially pronounced for the glasses containing MgO. We discuss these phenomena based on structural information obtained by NMR spectroscopy and topological considerations.

In this study, we present the preparation of a bulk material with a composition of 80GeTe₂–20Ga₂Te₃ by combining mechanosynthesis and sintering. This composition cannot be prepared by conventional melt/quenching technique. The progressive evolution of the powder during ball-milling is followed by X-ray Diffraction (XRD) and Differential Scanning Calorimetry analysis. The final powder obtained is highly crystalline, but a glass transition temperature (T_g) is observed, indicating the presence of some amorphous phase remaining, allowing for its efficient sintering. By hot-pressing, a dense bulk material with a fine microstructure and a high electrical conductivity is obtained. The synthesis method described represents a simple and cost-effective way to produce tellurium-based materials of desired dimension with potential applications for optical storage or thermoelectric devices.

Experimental studies have reported that zinc oxide improves the durability of glasses used for nuclear waste immobilization. Here, molecular dynamics simulations are used to predict the atomic structures of sodium silicate glass with and without zinc. A simulated melt-quench procedure is used to generate glass structures. Pair distribution functions, ring size distributions, and alkali clustering are then examined. This allows insights into the structural role of zinc oxide within the glass and helps distinguish between its reported functions as a network former and a network modifier. Changes in the sodium ion distribution and clustering behavior within the glass are observed, due to zinc oxide addition. This affects the local and intermediate-range structure of the glass and provides a possible explanation for enhanced durability.

Yttria partially stabilized zirconia Y-PSZ/glass-ceramic composites were prepared by reaction sintering using powder mixtures of a SiO₂–Al₂O₃–ZnO–CaO–ZrO₂–TiO₂-based glass and yttria partially stabilized zirconia (Y-PSZ). The glass crystallized during sintering at temperatures of 1173, 1273, and 1373 K to give a glass-ceramic matrix for high-temperature protecting coatings. With the increasing firing time, the added zirconia reacted with the base glass and a glass-ceramic material with dispersed zircon particles was prepared in situ. Furthermore, the added zirconia changed the crystallization behavior of the base glass, affecting the shape, amount, and distribution of zircon in the microstructure. The bipyramid-like zircon grains with imbedded residual zirconia particles turned out to have two growth mechanisms: the inward growth and the outward growth, and its rapid growth was mainly dominated by the later one. For comparison, the referenced glass-ceramic was prepared by sintering using exclusive glass granules and its crystallization behavior at 1173–1373 K was examined as well. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the crystallization behavior of the base glass and the phase evolution of the Y-PSZ/glass-ceramic composites.

In this article the changes on the surface of the 45S5 bioglass submitted to an enrichment with calcium ions were investigated. The method employed was the immersion of bioglass in calcium molten salt bath at 450°C. Changes in composition were probed by different techniques of chemical analysis. The use of SEM-EDS allowed estimating the thickness modified, as being about 10 μm. X-ray photoelectron spectroscopy enabled to infer over the structural changes on the surface of 45S5 bioactive glass. The entry of calcium in the vitreous network promoted the phase separation of microdomains rich in silica and phosphate on the surface of the glass. The formation of immiscibility region was attributed a depolymerization of silica network and also, to a possible migration of phosphate species from the bulk. The results of this study indicate a great change in the surface properties of this biomaterial. In addition, the method proposed in this study proved to be very promising in the possibility of designing the surface of bioactive glasses, to modulate the desired properties, keeping the bulk unchanged.

Glass formation behavior of the TeO₂–WO₃–Na₂O system was studied by using conventional melt-quenching technique. A wide glass formation range was determined for the first time in the literature and thermal, physical, and structural characterization of sodium-tungsten-tellurite glasses were realized using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. Glass transition (T_g) and crystallization (T_c/T_p) temperatures, glass stability (∆T), density (ρ), molar volume (V_M), oxygen molar volume (V_O), and oxygen packing density (OPD) values and structural transformations in the glass network were investigated according to the equimolar substitution of TeO₂ by Na₂O+WO₃ and changing Na₂O or WO₃ at constant TeO₂.

This study investigated the effects of the addition of Nb₂O₅ and sintering temperature on the properties of Bi₂Mo₂O₉ ceramics. The ceramics were sintered in air at temperatures ranging from 620°C to 680°C. The addition of small amounts of Nb₂O₅ as a dopant significantly affected the crystalline phase and the microwave dielectric properties of the Bi₂Mo₂O₉ ceramics. The secondary phase, γ-Bi₂MoO₆, was observed when Nb₂O₅ was added. However, unlike the Bi₂Mo₂O₉ ceramic without Nb₂O₅ sintered above 645°C, the ceramics with 3 mol% Nb₂O₅ contained no γ-Bi₂MoO₆ when sintered at 660°C. The Q × f value and τ_f of the Bi₂Mo₂O₉ ceramics were improved by Nb₂O₅ doping. The Bi₂Mo₂O₉ ceramics doped with 2 mol% Nb₂O₅ exhibited the best microwave dielectric properties, with a permittivity of 36.5, a Q × f value (f = resonant frequency, Q = 1/dielectric loss at f) of 14100 GHz and τ_f of +5.5 ppm/°C after sintering at 620°C.

Eu³⁺-activated borogermanate scintillating glasses with compositions of 25B₂O₃–40GeO₂–25Gd₂O₃–(10−x)La₂O₃–xEu₂O₃ were prepared by melt-quenching method. Their optical properties were studied by transmittance, photoluminescence, Fourier transform infrared (FTIR), Raman and X-ray excited luminescence (XEL) spectra in detail. The results suggest that the role of Gd₂O₃ is of significance for designing dense glass. Furthermore, energy-transfer efficiency from Gd³⁺ to Eu³⁺ ions can be near 100% when the content of Eu₂O₃ exceeds x = 4, the corresponding critical distance for Gd³⁺–Eu³⁺ ion pairs is estimated to be 4.57 Å. The strongest emission intensities of Eu³⁺ ions under both 276 and 394 nm excitation are simultaneously at the content of 8 mol% Eu₂O₃. The degree of Eu–O covalency and the local environment of Eu³⁺ ions are evaluated by the value of Ω_t parameters from Judd–Ofelt analysis. The calculated results imply that the covalency of Eu–O bond increases with the increasing concentration of Eu³⁺ ions in the investigated borogermanate glass. As a potential scintillating application, the strongest XEL intensity under X-ray excitation is found to be in the case of 6 mol% Eu₂O₃, which is slightly different from the photoluminescence results. The possible reason may be attributed to the discrepancy of the excitation mechanism between the ultraviolet and X-ray energy.

Impedance spectroscopy has been shown to be a powerful tool to investigate the dielectric characteristics of powders suspended in suitable liquids. The electrical and dielectrical contributions of different components of the slurry can be extracted from the impedance spectra through measurement of frequency-dependent relaxations. However, for ferroelectric powders that possess innate surface conductivity, such as BaTiO₃, nanoparticles have sufficient conductivity to exclude low-frequency fields that preclude impedance characterization of the particle core. In this work, the slurry technique is shown to be effective for dielectric characterization of not only micrometer-sized particles through equivalent circuit modeling but also applicable to nanometer size dielectric particles upon remediating the conductive surface defect. Application of a self-assembled monolayer (SAM) onto the nanoparticle as a surface passivation layer reduces the surface conductivity, stabilizes the nanoparticles to dissolution, and allows a reproducible measurement and modeling of the nanoparticle dielectric characteristics including nanoparticle permittivity. The dielectric permittivity of surface passivated, ~40 nm diameter barium titanate particles was measured to be ε_r ~ 135.

We, herein, present comparative investigations on the Na_0.5Bi_0.5Cu₃Ti₄O₁₂ ceramic samples with and without 10 mol% excess of Na/Bi. The samples were prepared by the standard solid-state reaction technique. The dielectric properties of the sample were investigated in the temperature (93–320 K) and frequency (20 Hz–10 MHz) windows. Three thermally activated dielectric relaxations observed in Na_0.5Bi_0.5Cu₃Ti₄O₁₂ with the activation energies of 0.104, 0.267, and 0.365 eV for the low-, middle-, and high-temperature dielectric relaxations, respectively. Only the low-temperature relaxation was observed in both Na and Bi excessive samples. X-ray photoemission spectroscopy results revealed the mixed-valent structures of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ in Na_0.5Bi_0.5Cu₃Ti₄O₁₂ sample, but only Ti³⁺/Ti⁴⁺ in Na and Bi excessive samples. Our results showed that the dielectric properties of the investigated samples are strongly linked with these mixed-valent structures. The high- and low-temperature relaxations were attributed to be a polaron-type relaxation due to localized carriers hopping between Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺, respectively. The middle-temperature relaxation is suggested to be a dipole-type relaxation caused by the defect complex of bismuth and oxygen vacancies.

The crystal structure and microwave dielectric properties of apatite-type LiRE₉(SiO₄)₆O₂ ceramics (RE = La, Pr, Nd, Sm, Eu, Gd, and Er) have been investigated. The densification of lithium apatites has been greatly improved with the addition of 1 wt% LiF. Selected area electron diffraction and X-ray diffraction (XRD) Rietveld analysis confirm that these compounds belong to the P6₃/m (No. 176) space group with hexagonal crystal symmetry. The porosity-corrected relative permittivity was found to decrease with decreasing ionic polarizability of RE³⁺ ions. Relationships between the structural parameters and microwave dielectric properties have been examined. The observed variation in the quality factor of LiRE₉(SiO₄)₆O₂ + 1 wt% LiF ceramics (RE = La, Pr, and Nd) was correlated with average cation covalency (%). The temperature coefficient of resonant frequency was found to depend on the bond valence sum of cations. LiEr₉(SiO₄)₆O₂ + 1 wt% LiF ceramics showed good microwave dielectric properties with ε_r = 12.8, Q_u × f = 13000 GHz and τ_f = +17 ppm/°C. All the compositions showed low coefficient of thermal expansion with thermal conductivity in the range 1.3–2.8 W (m K)⁻¹.

Acceptor-doped BaTiO₃ powders of formula: BaTi_1−xHo_xO_{3−x/2−δ/2}: x = 0.0001, 0.001, 0.01, 0.03, and 0.07, were prepared by sol-gel synthesis, fired at 800°C–1500°C and either quenched or slow-cooled to room temperature. Electrical properties of ceramics depended on firing conditions, Ho content, and cooling rate. Pellets of all x values fired at 800°C–1000°C were insulating and, from the presence of OH bands in the IR spectra, charge balance appeared to involve co-doping of Ho³⁺ and H⁺ ions without necessity for oxygen vacancy creation. At higher firing temperatures, OH bands were absent. Pellets fired at 1400°C in air and slow cooled were insulating for both low x (0.0001) and high x (0.07) but at intermediate x (0.001 and 0.01) passed through a resistivity minimum of 20–30 Ω cm at room temperature, attributed to the presence of Ti³⁺ ions; it is suggested that, for these dilute Ho contents, each oxygen vacancy is charge compensated by one Ho³⁺ and one Ti³⁺ ion. At higher x, charge compensation is by Ho³⁺ ions and samples are insulating. A second, more general mechanism to generate Ti³⁺ ions, and a modest level of semiconductivity, involves reversible oxygen loss at high temperatures.

We reported the dielectric properties of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ single crystal in the temperature range of 300–1073 K and the frequency range of 100 Hz–10 MHz. Our results showed the coexistence of both true- and pseudo-relaxor behaviors in the crystal. The true relaxor behavior related to the paraelectric-ferroelectric phase transition occurs at~423 K. The pseudo-relaxor behavior appearing at~773 K was found to be related to oxygen vacancies. Further investigation reveals that the pseudo-relaxor behavior has fine structure: it contains two oxygen-vacancy-related relaxation processes. The low-temperature relaxation process is a dipolar relaxation created by the hopping motions of the oxygen vacancies, and the high-temperature relaxation process is a Maxwell-Wagner relaxation caused by the sample/electrode contacts.

This article reports the structural and luminescence characteristics of Eu²⁺-activated solid solutions of (KSrPO₄)_1−x·((Ba,Sr)₂SiO₄)_x for 0 ≤ x ≤ 1. These phosphors were prepared by a sol-gel/Pechini method. The lattice parameters of the solid solutions are linearly dependent on x. The reliability factor from Rietveld analysis is nearly constant and independent of x, indicating KSrPO₄·(Ba,Sr)₂SiO₄ forms an ideal solid solution. The emission spectra consist of two distinct broad bands, which depend on x: blue ranging from 430 to 470 nm and green–yellow ranging from 515 to 570 nm. Both emission peaks red-shift as x increases due to the crystal field effect and an anomalous transition. The emission intensity of these solid solutions is also a function of x and is comparable to that of LiCaPO₄:Eu²⁺ (QE = 81%) at x = 0.1, suggesting that these color-tunable solid solutions are promising for applications in solid-state white lighting.

The 10 mol% ZnO–2 mol% B₂O₃–8 mol% P₂O₅–80 mol% TeO₂ (ZBPT) glass was prepared by quenching as well as slowly cooling the melt. The ZBPT glass prepared by both methods show similar microwave dielectric properties. ZBPT glass has an ε_r of 22.5 (at 7 GHz), Q_u × f of 1500 GHz, and τ_f of −100 ppm/°C. The ceramic-glass composites of Sr₂ZnTeO₆ (SZT) and ZBPT is prepared through two convenient methods: (a) conventional way of co-firing the ceramic with ZBPT glass powder and (b) a nonconventional facile route by co-firing the ceramic with precursor oxide mixture of ZBPT glass at 950°C. In the former route, SZT + 5 wt% ZBPT composite sintered at 950°C showed moderately good microwave dielectric properties (ε_r = 13.4, Q_u × f = 4500 GHz and τ_f = −52 ppm/°C). Although the SZT + 5 wt% ZBPT composite prepared through the nonconventional method also showed similar microwave dielectric properties (ε_r = 13.8, Q_u × f = 5300 GHz and τ_f = −50 ppm/°C), the synthesis procedure is much simplified in the latter case. The composites are found to be chemically compatible with Ag. The composite containing 5 wt% ZBPT prepared through conventional and nonconventional ways shows linear coefficients of thermal expansion of 7.0 ppm/°C and 7.1 ppm/°C, respectively. Both the composites have a room-temperature thermal conductivity of 2.1 Wm⁻¹ K⁻¹.

Diffusion properties of Tm³⁺ in congruent LiNbO₃ crystal have been investigated, together with other two related issues, i.e., Tm³⁺-doping contribution to refractive index of LiNbO₃ substrate and Li out-diffusion. Four X-cut and four Z-cut congruent LiNbO₃ substrates locally coated with 15–31 nm-thick Tm-metal films were annealed in surrounding air under different temperatures of 1030°C–1130°C for different durations of 20–70 h. After anneal, refractive index at Tm³⁺-doped and Tm³⁺-free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li₂O contents were evaluated from measured refractive index. The results show that Tm³⁺ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti⁴⁺- or Zn²⁺ doping. The Li₂O content at the Tm³⁺-doped surface equals that at the Tm³⁺-free surface. The Li out-diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out-diffusion is not measurable. At 1130°C, a 30-h diffusion procedure may cause 0.2–0.3 mol% slight loss of Li₂O content. Secondary ion mass spectrometry was used to study the Tm³⁺ diffusion properties. The results show that the diffused Tm³⁺ ions in all samples follow a complementary error function profile. From measured Tm³⁺ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er³⁺ diffusion. In comparison with Er³⁺ diffusion, the Tm³⁺ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm³⁺ has a lower diffusivity than the Er³⁺, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C.

A ternary ferroelectric ceramic system, (1−x−y)Pb(In_1/2Nb_1/2)O₃–xPb(Zn_1/3Nb_2/3)O₃–yPbTiO₃ (PIN–PZN–PT, x = 0.21, 0.27, 0.36, 0.42), was prepared using a two-step precursor method. The phase structure, dielectric, piezoelectric, and ferroelectric properties of the ternary ceramics were systematically investigated. A morphotropic phase boundary (MPB) was identified by X-ray diffraction. The optimum piezoelectric and electromechanical properties were achieved for a composition close to MPB (0.5PIN–0.21PZN–0.29PT), where the piezoelectric coefficient d₃₃, planar electromechanical coupling factor k_p, and remnant polarization P_r are 660 pC/N,72%, and 45 μC/cm², respectively. The Curie temperature T_C and rhombohedral to tetragonal phase transition temperature T_R−T were also derived by temperature dependence of dielectric measurements. The strongly “bended” MPB in the PIN–PT system was found to be “flattened” after addition of PZN in the PIN–PT–PZN system. The results demonstrate a possibility of growing ferroelectric single crystals with high electromechanical properties and expanded range of application temperature.

Barium hollandites, a family of framework titanates that can potentially be used for the immobilization of short-lived fission products (especially ¹³⁷Cs) in radioactive wastes, have been investigated by high-temperature oxide melt solution calorimetry using 2PbO·B₂O₃ solvent at 702°C. The enthalpies of formation from constituent oxides show increasing energetic stability of the hollandite phase as Ti⁴⁺ is substituted by Mg²⁺, Al³⁺, and Fe³⁺, in that order. In general, the thermodynamic stability increases with decreasing average cation radius in the β sites, and when the tolerance factor approaches one. The Al- and Fe-hollandites are more stable than phase assemblages containing BaTiO₃ perovskite and Al/Fe/Ti oxides, whereas Mg-hollandite is less stable than the corresponding assemblage of BaTiO₃ perovskite, MgTiO₃ ilmenite, and TiO₂. This instability makes Mg-hollandite a less suitable host for fission products. Hollandite phase formation during metal citrate combustion synthesis depends more on thermodynamic stability and phase chemistry than on the annealing temperature.

Graphene/Bi₂WO₆ composites have been synthesized by hydrothermal reduction at 160°C for 24 h using ethanol as the reducing agent. All as-prepared composites were characterized using X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, FT-IR spectroscopy, Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, N₂ adsorption, and photocatalytic activity evaluation. The effective charge separation of graphene/Bi₂WO₆ composites was caused by the electrical conduction of graphene which is the most important factor. The results have proved the formation of interfacial contact between graphene nanosheets and Bi₂WO₆ nanoplates. The adsorptivity for azo dyes was enhanced greatly with the introduction of graphene. The oxy-functional groups located at the edges of graphene were responsible for the enhanced adsorptivity. As-prepared graphene/Bi₂WO₆ composites exhibited enhanced light absorption from UV to visible-light region. In addition, the introduction of graphene would also result in smaller crystalline size and lower crystallinity of Bi₂WO₆. Graphene/Bi₂WO₆ composites containing an appropriate amount of graphene were proved to exhibit higher adsorptivities and photocatalytic activities for azo dyes. High photocatalytic activities of graphene/Bi₂WO₆ composites were considered to be the synergetic effects of high adsorption, high light absorption, and high electrical conduction induced by the introduction of graphene.

The oxidation behaviors of ZrB₂- 30 vol% SiC composites were investigated at 1500°C in air and under reducing conditions with oxygen partial pressures of 10⁴ and 10⁻⁸ Pa, respectively. The oxidation of ZrB₂ and SiC were analyzed using transmission electron microscopy (TEM). Due to kinetic difference of oxidation behavior, the three layers (surface silica-rich layer, oxide layer, and unreacted layer) were observed over a wide area of specimen in air, while the two layers (oxide layer, and unreacted layer) were observed over a narrow area in specimen under reducing condition. In oxide layer, the ZrB₂ was oxidized to ZrO₂ accompanied by division into small grains and the shape was also changed from faceted to round. This layer also consisted of amorphous SiO₂ with residual SiC and found dispersed in TEM. Based on TEM analysis of ZrB₂–SiC composites tested under air and low oxygen partial pressure, the ZrB₂ begins to oxidize preferentially and the SiC remained without any changes at the interface between oxidized layer and unreacted layer.

A new class of layered microstructural composites that combines equiaxed and textured alumina layers was fabricated. Template loading was used to change the texture fraction and porosity in the textured layers. Due to the thermal expansion anisotropy of the textured layers, residual compressive stresses as high as 100 MPa were achieved during cooling from the sintering step. Fracture experiments showed that the interface between the basal planes of highly oriented alumina grains in the textured layers changes from a “strong interface” to a “weaker interface” as the porosity changes from 1% to 5%. Composites with 5% porous textured layers show both crack bifurcation and crack deflection in the textured layers. Crack deflection is attributed to the anisotropic fracture energy of the oriented microstructures and crack bifurcation is ascribed to the compressive stresses that arise from the thermal expansion mismatch between adjacent layers.

The reduction in fiber push-out stress by transformation plasticity in xenotime rare-earth orthophosphate fiber–matrix interphases was demonstrated. Processing methods for transformable xenotime coatings were explored. For conversion to xenotime during processing, (Gd_xDy_1−x)PO₄ solid solutions had to be more Dy-rich than those for pellets. Single-crystal alumina fibers were coated with 10–20 μm of (Gd_0.4Dy_0.6)PO₄ xenotime and incorporated into polycrystalline alumina matrices. Coated fiber push-out stresses were between 10 and 80 MPa, significantly lower than those for fibers with other rare-earth orthophosphates coatings. Phase transformations and deformation mechanisms were characterized by SEM and TEM in fiber coatings after push out. Bands of deformed coating several micrometers in width formed during fiber push out. Cataclastic flow with fracture, granulation, translation, rotation, and intense plastic deformation of coating grains was observed. Three phase transformations may occur in heavily deformed particles in the deformation band: xenotime → monazite, xenotime → anhydrite, and anhydrite → monazite. Anhydrite was abundant as a fine lamellar phase on (100) planes in xenotime. Selected area electron diffraction and high-resolution TEM confirmed formation of monazite in a variety of heavily deformed particles. Issues for use of rare-earth orthophosphate transformation plasticity to lower fiber pull-out stress in ceramic matrix composites are discussed.

Photocatalytic and hydrophilic TiO₂ thin-film applications include water purification, cancer therapy, solar energy conversion, self-cleaning devices, and antifogging windows. We demonstrate superhydrophilicity of aerosol-deposition (AD) TiO₂ films on a glass substrate without use of a carrier solvent, thereby removing the possibility of impurity contamination. AD films exhibit high visible light transmittance (greater than 80%) and superhydrophilicity (0° contact angle) with even minimal UV-light irradiation exposure. This AD method represents a significant step toward the realization of economically viable, functional thin films for the aforementioned applications.

A series of Dy³⁺–Eu³⁺-codoped ZrO₂ nanocrystals with tetragonal and cubic symmetry was synthesized via a wet chemical reaction. When the Eu³⁺-doping content was fixed, the crystal structure could be stabilized from the mixed phase to single cubic phase by simply adjusting the content of Dy³⁺. The cubic ZrO₂:Dy³⁺–Eu³⁺ nanoparticles exhibited spherical and nonagglomerated morphology. The effective phonon energy of cubic ZrO₂:5%Dy³⁺–5%Eu³⁺ was calculated to be 445 cm⁻¹, which is lower than the previously reported results. Extensive luminescence studies of ZrO₂:Dy³⁺–Eu³⁺ as a function of Dy³⁺ content demonstrated that the dopant concentration and its site symmetry play an important role in the emissive properties. Under 352 nm excitation, the increment of Dy³⁺ concentration in ZrO₂:Dy³⁺–Eu³⁺ led to an increase in orange (590 nm) and red (610 nm) emissions of Eu³⁺ ions, which are attributed to the ⁵D₀→⁷F_J(J = 1, 2) transitions of Eu³⁺ ions. This increment is possibly due to the efficient energy transfer (ET) ⁴F_9/2:Dy³⁺→⁵D₀:Eu³⁺. The phosphors can generates light from yellow through near white and eventually to warm white by properly tuning the concentration of Dy³⁺ ions through the ET and change in site symmetry. These phosphors may be promising as warm-white-/yellow-emitting phosphors.

SiC coatings in tri-structural isotropic-coated (TRISO) particles were thermally treated at 2000°C for 1 h in argon atmosphere. The fracture strength of the SiC decreased while change in the Weibull modulus of the failure strength is more complex after the thermal treatment. The variation in both fracture strength and Weibull modulus can be explained by the formation of the pores in SiC due to thermal treatments, as annihilation of the stacking faults and diffusion of intrinsic defects lead to the pore formation.

Single-crystalline potassium tungsten bronze nanosheets were prepared by reducing potassium tungsten oxide nanosheets grown on a W foil. The nanosheets showed no evident shape change before and after reduction. Morphology, structure, and composition analyses revealed that a phase transformation from orthorhombic potassium tungsten oxide to hexagonal potassium tungsten bronze occurred. Better field emission with lower turn-on field was measured from potassium tungsten bronze nanosheet film. The effects of reduction treatment on field emission performance are discussed.

Third-generation SiC fibers [High Nicalon S (HNS) and Tyranno SA3 (Ty–SA3)] were studied by X-ray diffraction and transmission electron microscopy (TEM) after heat treatments in neutral atmosphere up to 1900°C. The microstructural changes in both materials were determined using a modified Hall–Williamson method introducing an anisotropy parameter taking into account the high density of planar defects. HNS fibers exhibit significant modifications in the coherent diffraction domains (CDD) size, which drastically increases from 24 to 70 nm in the range 1600°C–1900°C. TEM observations support these results. The residual microstrain values decrease from 0.0015 to 0.0005 between 1750°C and 1850°C. Similarly, the anisotropy parameter significantly decreases in the same temperature range. Concerning the Ty–SA3 fibers, no evolution in terms of CDD size and residual microstrain was observed. However, the anisotropy parameter decreases at 1800°C. TEM observations did not show noticeable grain growth. The grain size was found to be larger than the CDD and the planar defects density to decrease at high temperature. In both types of fibers, the CDD sizes are similar for the highest temperature heat treatments.

Ce_0.6Zr_0.4O₂ (C60Z) powders were synthesized using the chemical coprecipitation method to investigate the phase separation mechanism. The phase separation of C60Z powders occurred during the heating step (>1100°C), suggesting that it might be a thermally activated process. The activation energy for the phase separation of C60Z was 398 (±20) kJ/mol and the Avrami parameter was ~1.0, indicating that the phase separation may be interface controlled. We suggested that Zr⁺⁴ diffusion played an important role in C60Z phase separation due to the ionic radius of Zr⁺⁴ being smaller than that of Ce⁺⁴. The C60Z powders tended to aggregate, which induced the driving force for the phase separation resulting from the surface energy difference between the particle surface and the interface. The phase separation behavior of C60Z powders was very similar to the initial stage of sintering. After high-temperature treatment, more Zr⁺⁴ ions diffused to the interface between C60Z particles to lower the surface energy of the system than did Ce⁺⁴ ions, which resulted in the composition gradually being changed and phase separation. Therefore, the phase separation of C60Z powders can be effectively decreased by the addition of Al⁺³, which suppresses aggregation.

Using synchrotron X-ray diffraction and diamond anvil cells we performed in situ high-pressure studies of mullite-type phases of general formula Al_4+2xSi_2−2xO_10−x and differing in the amount of oxygen vacancies: 2:1-mullite (x = 0.4), 3:2-mullite (x = 0.25), and sillimanite (x = 0). The structural stability of 2:1-mullite, 3:2-mullite, and sillimanite was investigated up to 40.8, 27.3, and 44.6 GPa, respectively, in quasi-hydrostatic conditions, at ambient temperature. This is the first report of a static high-pressure investigation of Al₂O₃–SiO₂ mullites. It was found that oxygen vacancies play a significant role in the compression mechanisms of the mullites by decreasing the mechanical stability of the phases with the number of vacancies. Elevated pressure leads to an irreversible amorphization above ~20 GPa for 2:1-mullite and above 22 GPa for 3:2-mullite. In sillimanite, only a partial amorphization is observed above 30 GPa. Based on Rietveld structural refinements of high-pressure X-ray diffraction patterns, the pressure-driven evolution of unit cell parameters is presented. The experimental bulk moduli obtained are as follows: K₀ = 162(7) GPa with K₀′ = 2.2(6) for 2:1-mullite, K₀ = 173(7) GPa with K₀′ = 2.3(2) for 3:2-mullite, K₀ = 167(7) GPa with K₀′ = 2.1(4) for sillimanite.

Amorphous bioactive glasses such as 45S5 have been successfully used in bone-filling therapy in non-load bearing biomedical applications for decades. In this study, we challenge the predilection to amorphous over crystalline ceramics by investigating the effect of synthesis route on surface texture, in vitro dissolution, and mineral formation on powders produced by sol–gel and glass melt-casting methods. Many reports have indicated bulk crystalline bioactive glass-ceramics to be less bioactive than their amorphous counterparts as measured by the onset time for mineral formation. Bioactive glass 45S5 was synthesized using the sol–gel method followed by heat treatment to produce a semi-crystalline structure and was compared against commercially available amorphous melt-cast 45S5 powder. Gel-derived samples were stabilized at 700°C making more than 80% of the structure crystalline. Dissolution of 45S5 glass-ceramic in powder form(particle diameter 12 μm) was studied by in vitro immersion in simulated body fluid solution for various periods of time. The immersed powders were then analyzed through X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), Differential scanning calorimetry (DSC), and thermogravimetric analysis (DSC/TGA), and Fourier transform infrared spectroscopy (FTIR) to determine the onset time for surface mineralization, and were compared with the melt-cast powder as a control. The rates of dissolution and onset time for mineral formation were similar for the gel-derived powder as compared with the melt-cast control; it is proposed that the higher surface area of the sol–gel powder overcame the penalty usually associated with lower dissolution rates of crystalline materials, implicating surface texture as a much more important determinant of dissolution and mineralization behavior than mere crystallinity.

A comparative structural study of silicon borocarbonitride polymer-derived ceramics synthesized using polyborosilylcarbodiimide and polyborosilazane precursors is carried out using high-resolution, multinuclear, one- and two- dimensional NMR spectroscopy. The polyborosilylcarbodiimide-derived ceramics contain relatively pure Si₃N₄ and C nanodomains with the BN domains being present predominantly at the interface such that the bonding at the interface consists of Si–N–B, Si–N–C, and B–N–C linkages. In contrast, the structure of the polyborosilazane-derived ceramics consists of significant amount of mixed bonding in the nearest-neighbor coordination environments of Si and B atoms leading to the formation of SiC_xN_4−x (0 ≤ x ≤ 4) tetrahedral units and BCN₂ triangular units. The interfacial region between the SiCN and C nanodomains is occupied by the BCN phase. These results demonstrate that the chemistry of the polymeric precursors exerts major influence on the microstructure and bonding in their derived ceramics even when the final chemical compositions of the latter are similar.

The microstructures of the Bi_0.4Ca_0.6MnO₃ (BCMO) and La_0.67Ca_0.33MnO₃ (LCMO) epitaxial films are investigated by transmission electron microscopy in detail. BCMO epitaxial films (~ 10 and ~ 40 nm) exhibit an island growth mode whereas the LCMO films (~ 6 and ~ 30 nm) follow a layer by layer growth mode. Combined with the critical thickness models for the expected onset of the misfit dislocations in epitaxial films, an atomic collapse model is introduced to explain their mechanism of formation in manganite films. At the beginning of deposition, the strain caused by the lattice mismatch between the epitaxial film and substrate can be accommodated by elastic deformation. With the increase of film thickness, the strain becomes larger and larger. When the film thickness reaches the critical thickness, the strain can only be relaxed by the formation of misfit dislocations. Meanwhile, the atomic configuration of the epitaxial film will reorganize and some atoms begin to collapse, thus an island morphology will be formed. Once the collapse morphology is formed, maintenance of this wave-like morphology depends on atomic diffusion length of the deposited atoms. If the diffusion length of the deposited atoms is long, the island morphology will not be maintained. If the diffusion length of the deposited atoms is short, the island morphology will keep until the epitaxial film is thick enough. The results could shed light on the growth modes for other perovskite epitaxial films.

Thin films of nanocrystalline ceria deposited onto a silicon substrate have been irradiated with 3 MeV Au⁺ ions to a total dose of 34 displacements per atom to examine the film/substrate interfacial response upon displacement damage. Under irradiation, a band of contrast is observed to form that grows under further irradiation. Scanning and high-resolution transmission electron microscopy imaging and analysis suggest that this band of contrast is a cerium silicate phase with an approximate Ce:Si:O composition ratio of 1:1:3 in an amorphous nature. The slightly nonstoichiometric composition arises due to the loss of mobile oxygen within the cerium silicate phase under the current irradiation condition. This nonequilibrium phase is formed as a direct result of ion-beam-induced chemical mixing caused by ballistic collisions between the incoming ion and the lattice atoms. This may hold promise in ion beam engineering of cerium silicates for microelectronic applications e.g., the fabrication of blue LEDs.