Temperature-stable and ultralow-loss (1 − x)CaSmAlO₄–xSr₂TiO₄ microwave dielectric solid-solution ceramics

The (1 − x)CaSmAlO₄–xSr₂TiO₄ (0.01 ≤ x ≤ 0.06) microwave dielectric ceramics were for the first time prepared by a conventional solid-state method. The phase composition, sintering behavior, microstructure and microwave dielectric properties were investigated as function of sintering temperature and composition. A single-phase solid solution with K₂NiF₄-type tetragonal structure was formed in the range of 0.02 ≤ x ≤ 0.06. All samples are well densified with very little pores. The addition Sr₂TiO₄ greatly improves dielectric properties originally by restraining the secondary phase and then deteriorates Q × f value because of decreasing tolerance factor. Moreover, the τ_f value dominated by the thermal expansion coefficient increases lineally as x rises. Finally, excellent microwave dielectric properties of ε_r ~ 18.1, Q × f ~ 140,433 GHz (8.5 GHz), and a near-zero τ_f ~  + 0.05 ppm/°C can be obtained in the x = 0.05 ceramic sintered at 1425 °C.