Mixture behavior and microwave dielectric properties of (1 − x)CaWO4–xTiO2

The microwave dielectric characteristics and mixture behavior of (1 − x)CaWO4–xTiO2 ceramics prepared with conventional solid-state route were studied using a network analyzer and X-ray power diffraction, respectively. The CaWO4 compound had good properties (low permittivity and high quality factor) for microwave applications, but it had a high negative temperature coefficient of resonant frequency (τf = −53). Hence, in order to tune the dielectric properties, (1 − x)CaWO4–xTiO2 were prepared for different values of x. X-ray powder diffraction and SEM analysis revealed that CaWO4 and TiO2 coexisted as a mixture. The mixture formation and dielectric properties could be explained by mixture rule. In particular, at x = 2.6, good microwave dielectric properties were obtained: Qf = 27,000, ɛr = 17.48, and τf = ∼0 ppm/°C.