Structure refinement, defects evolution and calcium doping of Sr2CeO4 microwave dielectric ceramics with high quality factor.

Sr 2-2 x Ca 2 x CeO 4 (x = 0, 0.025, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8) ceramics were synthesized through cold isostatic pressing and solid-state reaction. The microstructure, defects, microwave dielectric properties, and the effect of Ca2+ doping of Sr 2 CeO 4 ceramics were systematically investigated. As the sintering temperature increased, the densities of Sr 2 CeO 4 ceramics rose, the content of oxygen vacancies increased, and Ce4+ reduction would be enhanced. In addition, the Sr 2 CeO 4 structure had poor compatibility with Ca2+. The major phase could be kept unchanged only when x ≤ 0.1. The reason was that the doping of Ca2+ intensified the distortion of the CeO 6 octahedron and induced the structural transformation of the common edges (Sr 2 CeO 4) to the common angles (SrCeO 3). With the increase of dopant, the densities of Sr 2-2 x Ca 2 x CeO 4 ceramics increased significantly, while the content of oxygen vacancies also increased. The microwave dielectric properties were mainly influenced by the density, structural symmetry, defects, and the second phase SrCeO 3. The dielectric permittivity (ε r) of 13.4–15, the quality factor (Qf) of 118,580–52,170 GHz, and the temperature coefficient of resonant frequency (τ f) of −58.3 ∼ −47.5 ppm/°C were obtained for Sr 2-2 x Ca 2 x CeO 4 ceramics When x ≤ 0.1. This work has provided a foundation for further research on cerate microwave dielectric ceramics. [ABSTRACT FROM AUTHOR]