Structure refinement, defects evolution and calcium doping of Sr2CeO4 microwave dielectric ceramics with high quality factor. Issue 18 (15th September 2022) - Zhang, Ao
Abstract: Sr2-2 x Ca2 x CeO4 ( 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 Ca 2+ doping of Sr2 CeO4 ceramics were systematically investigated. As the sintering temperature increased, the densities of Sr2 CeO4 ceramics rose, the content of oxygen vacancies increased, and Ce 4+ reduction would be enhanced. In addition, the Sr2 CeO4 structure had poor compatibility with Ca 2+ . The major phase could be kept unchanged only when x ≤ 0.1. The reason was that the doping of Ca 2+ intensified the distortion of the CeO6 octahedron and induced the structural transformation of the common edges (Sr2 CeO4 ) to the common angles (SrCeO3 ). With the increase of dopant, the densities of Sr2-2 x Ca2 x CeO4 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 SrCeO3 . 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 Sr2-2 x Ca2 x CeO4 ceramics When x ≤ 0.1. This work has provided a foundation for further research on cerate microwave dielectric ceramics.