Structure evolution and microwave dielectric characteristics of Ca[(AlxGa0.5-xNb0.5)0.5Ti0.5]O3 ceramics

The microwave dielectric characteristics of Ca[(AlxGa0.5-xNb0.5)0.5Ti0.5]O3 (x = 0, 0.1, 0.2, 0.4, 0.5) ceramics were investigated together with the structure evolution. Distorted perovskite structure in space group Pbnm with b-b-c+ tilting was determined for the present solid solutions, where the microstructures were remarkably affected by Al-content. Owing to the Al-substitution which was accompanied by the subdued octahedral tilting, the Qf value reached up to 40,000 GHz with increasing x, the dielectric constant (εr) remained at around 50, and the temperature coefficient of resonant frequency (τf) could be adjusted to near zero. Low-loss temperature-stable microwave dielectric ceramics with medium dielectric constant were obtained at x = 0.2-0.5, which exhibited Qf values of 35,900-40,000 GHz, εr of 49.2-53.4, and τf of 0.6-3.5 ppm/°C.