Sm2-xCexO3+x/2 Composite microwave dielectric ceramics with tunable τf and enhanced Q×f

Dense Sm2-xCexO3+x/2 (x = 0.10−0.25) ceramics were obtained by the solid-state method. Main-phase Sm2O3 with monoclinic structure and a small amount of fluorite-structured CeO2 were achieved. As the x value increased, the τf significantly reduced from 18.8 ± 2.0 ppm/°C to −20.3 ± 2.0 ppm/°C and the Q×f enhanced from 21,382 ± 300 to 32,927 ± 300GHz. The τf variating from positive to negative was related to the increasing temperature coefficient of ion polarizability (ταm) from 20.6 ppm/°C to 27.9 ppm/°C. The rise in Q×f was attributed to the reduced AC conductivity resulting from the decreasing oxygen vacancy concentration. The addition of Ce could effectively inhibit the decomposition of Sm2O3 ceramics in atmospheric condition. Notably, the Sm1.80Ce0.20O3.10 ceramic sintered at 1475 °C demonstrated optimal microwave dielectric properties of εr = 19.2 ± 0.2, Q×f = 28,033 ± 300GHz, and τf = 1.8 ± 2.0 ppm/°C.