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Designing of Glass-Free LTCC Microwave Ceramic- Ca1−x(Li0.5Nd0.5)xWO4 by Crystal Chemistry


  • This work was supported by the National Science Foundation of China (NSFC), (project number: 50872081)

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Designing guidelines for glass-free low-temperature cofired ceramic (LTCC) materials were proposed from the point of view of crystal chemistry. As an example, Ca1−x(Nd0.5Li0.5)xWO4 was successfully designed as glass-free LTCC materials by crystal chemistry. The sintering behavior, microstructure, and microwave dielectric properties of Ca1−x(Nd0.5Li0.5)xWO4 ceramics were investigated in this study. The structure and microstructure of the compounds were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 9–13 GHz. Continuous solid solutions Ca1−x(La0.5Na0.5)xWO4 (0.1 ≤ x≤0.5) were formed as expected in the experimented composition range. They could be sintered into dense ceramics (approximately 96%–98% theoretical density) at 825°C–875°C per 2 h. All samples exhibit Scheelite structure (I41/a) phase. Both of the sintering temperature and microwave dielectric properties, especially the temperature coefficient of resonant frequency (τf), could be tuned in a wide range. Combined excellent microwave dielectric properties with εr = 11.7, Q × f = 36 700 GHz, and τf = 5.36 ppm/°C could be obtained for the x = 0.2 composition after sintering at 825°C/2 h. The chemical compatibility of Ca0.8(Nd0.5Li0.5)0.2WO4 ceramic with silver (Ag) powders was also investigated. No chemical reaction has taken place between the matrix phase and Ag after sintering at 850°C/2 h. Thus, it can be used as a promising glass-free microwave dielectric material for LTCC applications.