Designing of Glass‐FreeLTCCMicrowave Ceramic‐Ca1−x(Li0.5Nd0.5)xWO4by Crystal Chemistry

Abstract

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)xWO4was successfully designed as glass‐freeLTCCmaterials by crystal chemistry. The sintering behavior, microstructure, and microwave dielectric properties ofCa1−x(Nd0.5Li0.5)xWO4ceramics were investigated in this study. The structure and microstructure of the compounds were investigated byX‐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 solutionsCa1−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, andτf = 5.36 ppm/°C could be obtained for thex = 0.2 composition after sintering at 825°C/2 h. The chemical compatibility ofCa0.8(Nd0.5Li0.5)0.2WO4ceramic with silver (Ag) powders was also investigated. No chemical reaction has taken place between the matrix phase andAgafter sintering at 850°C/2 h. Thus, it can be used as a promising glass‐free microwave dielectric material forLTCCapplications.