Microstructure and microwave dielectric characteristics of the Ca_xZn_1−xTiNb₂O₈ temperature stable ceramics

The quantitative determination and the crystal structure of Ca_xZn_1−xTiNb₂O₈ ceramics were analyzed by X-ray diffraction, the microwave dielectric properties were investigated. The results showed that the Ca_xZn_1−xTiNb₂O₈ ceramics contained three main phases: ZnTiNb₂O₈ phase Zn_0.17Nb_0.33Ti_0.5O₂ phase and CaNb₂O₆ phase. With the increase of Ca content, the weight fraction of secondary phase Zn_0.17Nb_0.33Ti_0.5O₂ and CaNb₂O₆ increased. For ZnTiNb₂O₈, with the substitution of Ca²⁺ for Zn²⁺, the bond valence of Ti-site increased. The variation of distortion of oxygen octahedral was irregular. For Zn_0.17Nb_0.33Ti_0.5O₂, the distortion of oxygen octahedral and the bond valence of Ti-site increased with substitution of Ca²⁺. The increase of Ti-site bond valence led to a harder rattling of Ti cations of the specimens. As a result, the dielectric constant (ε) and the quality factor value (Qf) decreased, the temperature coefficient of resonant frequency (τ _f ) moved to the positive direction. The typical values of ε = 38.6, Qf = 41,338 GHz, τ _f  = −1.28 × 10⁻⁶/°C were obtained for Ca_xZn_1−xTiNb₂O₈ (x = 0.45) specimens sintered at 1100 °C for 6 h. The high dielectric properties in microwave range drive these materials a promising application in electronics.