Improvement in microwave dielectric properties of Sr2TiO4 ceramics through post-annealing treatment

Abstract

Sr2TiO4 ceramics were synthesized via the conventional solid-state reaction process, and the effects of post-annealing treatment in air on the microwave dielectric properties and defect behavior of title compound were investigated systematically. The Q × f values could be effectively improved from 107,000 GHz to 120,300 GHz for the specimens treated at 1450 °C for 16 h. The thermally stimulated depolarization currents (TSDC) revealed two kinds of defect dipoles [ $$ \left({\mathrm{Ti}}_{\mathrm{Ti}}^{\hbox{'}}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ and $$ \left({V}_{\mathrm{Sr}}^{"}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ ] and oxygen vacancies $$ \left({V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ were considered the main defects in Sr2TiO4. Under a post-annealing treatment in air, the concentrations of such defects in the ceramics decreased. Meanwhile, the impedance spectrum revealed the activation energy of the grain boundaries increased. These evidences could account for the improvement of Q × f values. Accompanied with a high er of 40.4 and a large τf of 126 ppm/°C, the enhanced high-Q Sr2TiO4 ceramics can be good candidates for applications in wireless passive temperature sensing.