Microstructure and crystal structure dependence of microwave dielectric properties of non-stoichiometric (Sr0.7Ca0.3)z(Zr0.95Ti0.05)O3 perovskite ceramics.

Solid-state reaction process has been used to fabricate (Sr 0.7 Ca 0.3) z (Zr 0.95 Ti 0.05)O 3 (0.98 ≤ z ≤ 1.04) ceramics, the effects of non-stoichiometric ratio on sintering behavior, microstructure, structural properties and microwave dielectric properties were investigated. The ceramics contain the secondary phase ZrO 2 with Fm-3m and P42 space structure as z ≤ 1.01. Electron back scatter diffraction analysis indicates that the secondary phase is concentrated at the grain boundary, which hinders the grain growth. Based on Rietveld refinement and Raman spectra, the secondary phase content and structural characteristics, including cell parameters, polarizability and lattice vibration anharmonicity, are obtained to establish the correlation between structure and microwave dielectric properties. The relative permittivity depends on the polarizability, and the variation of Q × f values is determined by the combined effects of grain size, secondary phase and lattice intrinsic loss, and is mainly driven by lattice vibration anharmonicity. In addition, the τ f values are affected by lattice distortion. Particularly, (Sr 0.7 Ca 0.3) 1.02 (Zr 0.95 Ti 0.05)O 3 (z = 1.02) ceramics have the optimized microwave dielectric properties: ε r = 35.9, Q × f = 26,000 GHz, τ f = −13 ppm/°C. This work provides a reference for optimizing microwave dielectric properties of materials. [ABSTRACT FROM AUTHOR]