New SrSmGa3O7 Ceramics: Sintering Behavior, Structure, Electrical, and Microwave Dielectric Properties

The development of high-frequency communication technology urgently requires new types of microwave dielectric ceramics with excellent performance. New melilite-structured SrSmGa 3 O 7 ceramics were prepared by using the conventional solid-state method. The impedance analysis demonstrates that SrSmGa 3 O 7 ceramics have good insulation characteristics, with the conducting activation energies of 0.51 and 1.01 eV for the grain and grain boundary, respectively. The bond valence theory suggests that the stretched Sm–O and Ga–O bonds have a major influence on ε r, leading to a higher measured value than the theoretical one (7.6). The calculation by P–V–L chemical bond theory shows that the Sr/Sm–O bond significantly affects the bond ionicity ( f i ), and the Ga–O bonds have a crucial influence on the lattice energy ( U b ) and bond energy ( E b ). This result provides guidance for SrSmGa 3 O 7 ceramic modification to enhance its performance. The 1425 °C sintered SrSmGa 3 O 7 ceramic exhibited the optimal microwave dielectric properties (ε r = 12.1 ± 0.1, Q × f = 27,740 ± 613 GHz (at 11.4 GHz), and τ f = −37.5 ± 0.4 ppm/°C), indicating that the SrSmGa 3 O 7 ceramics are a favorable dielectric material for high-frequency applications.