[en] Highlights: • The crystal structure of Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics were analyzed. • The quantitative determination of Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics were analyzed. • The typical values of ε = 53.09, Qf = 48,000 GHz, τ_f = 21.20 ppm/°C were obtained. -- Abstract: The quantitative determination and the crystal structure of Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics were analyzed by X-ray diffraction, the microwave dielectric properties were investigated. The results showed that the Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics contained three main phases: ZnTiNb₂O₈ phase, Zn_0.15Nb_0.30Ti_0.55O₂ phase and Unknown Columbite-type phase. With the increase of Ca content, the weight fraction of secondary phase Zn_0.15Nb_0.30Ti_0.55O₂ and Unknown Columbite-type phase 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_0.15Nb_0.30Ti_0.55O₂, 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 = 53.09, Qf = 48,000 GHz, τ_f = 21.20 ppm/°C were obtained for Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ (x = 0.02) specimens sintered at 1120 °C for 6 h. The relative low sintering temperature and high dielectric properties in microwave range make these ceramics promising for application in multilayer ceramic capacitors

[en] Highlights: • BaCu(B₂O₅) is added to the multi-ions doped SrTiO₃ ceramics as sintering aid. • The sintering temperature is decreased from 1300 °C to 1075 °C. • The incorporation of Ba²⁺ into the matrix increases the dielectric constant. • The breakdown strength increases due to the decrease of grain size and porosity. • The dissolution of BCB contributes to the improvement of dielectric properties. -- Abstract: BaCu(B₂O₅) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO₃ ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu²⁺ and Ba²⁺, while further increase was owing to the increase of dissolved Ba²⁺ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO₃ ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm³ and energy efficiency of 98.83%