Effect of Ca substitution on phase compositions and dielectric properties of Bi₂O₃-ZnO-Nb₂O₅ pyrochlore ceramics

The phase evolution, microstructure and dielectric properties in the Ca²⁺ substituted Bi₂O₃-ZnO-Nb₂O ₅ system were studied. The crystalline phases of the [Bi _1.8(Ca_xZn_1-x)_0.2](Zn _0.6Nb_1.4)O₇ pyrochlores (0.0≤x≤1.0) depend greatly on the ratio of ionic radius A/B. With the Ca²⁺ substitution for Zn²⁺ in the A site, the crystalline phase transformed from cubic to monoclinic and pure monoclinic phase was obtained for x≥0.5. As the x value increased from 0.5 to 1.0, the permittivity in the microwave range decreased from 76.4 to 75.0, the quality factor Qf value increased from 1800 to 4700 GHz, and the TCF value shifted from -99 to -147 ppm/°C.