Preparation and microwave dielectric properties of cristobalite ceramics

Dense SiO₂ ceramics with cristobalite phase were prepared by the solid state sintering route, and the microwave dielectric properties were evaluated. The dielectric constant (?_r) and temperature coefficient of resonant frequency (τ_f) of the pure cristobalite ceramics showed little dependence on the sintering temperature. While, the Qf value increased significantly with increasing the sintering temperature, and it was due to the increasing grain size. The optimized microwave dielectric properties with very low ?_r of 3.81, high Qf value of 80,400 GHz and low τ_f of ?16.1 ppm/°C were obtained for the cristobalite ceramics sintered at 1650 °C for 3 h. It was indicated that cristobalite ceramic was a promising candidate as a low-dielectric-constant microwave material for applications in microwave substrates.