Microwave dielectric properties and microstructures of xBa_0.33Sr_0.67TiO₃–(1−x)Ba₄Sm_9.33Ti₁₈O₅₄ ceramics with near-zero temperature coefficient

The phase composition, microstructures, sintering behavior, and microwave dielectric properties of Ba_0.33Sr_0.67TiO₃–Ba₄Sm_9.33Ti₁₈O₅₄ ceramics prepared via conventional solid-state route were systematically investigated as a function of the Ba_0.33Sr_0.67TiO₃ molar fraction and sintering temperature. All the sintered ceramics only exhibited a single orthorhombic tungsten bronze structure BaSm₂Ti₄O₁₂ phase. And all samples sintered at 1400 °C showed fully dense and homogeneous microstructures. The variation of bulk density and dielectric properties are related with the Ba(Zn_1/3Nb_2/3)O₃ molar fraction, but not with a same trend. As Ba ions in A1 sites are substituted by Sr ions, Q × f values enhanced dramatically. The optimum microwave dielectric properties with an ε_r value of 80.13, a Q × f value of 11386 GHz (at 3.5 GHz), and a τ_f value of − 0.34 ppm/°C were obtained for 0.03Ba_0.33Sr_0.67TiO₃–0.97Ba₄Sm_9.33Ti₁₈O₅₄ ceramics sintered at 1400 °C for 4 h.