Processing and Properties of Eu3+-Doped Barium Bismuth Titanate (BaBi4Ti4O15) Glass–Ceramic Nanocomposites


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Precursor glasses for the ferroelectric barium bismuth titanate (BaBi4Ti4O15) (BBiT) have been prepared by the melt-quench technique in the SiO2K2OBaOBi2O3TiO2 (SKBBT) glass system with and without Eu2O3 doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm−1. The activation energy of crystallization (Ec) varies from 295 to 307 kJ/mol. The dielectric constants (εr) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat-treated GCs show higher εr values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5D07F2 transition. An intense 466 nm excitation band corresponding to the 7F05D2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam0.5) values obtained in the GCs are high and suitable for structural applications.