Microwave dielectric properties of BaWO4-doped Ba(Mg1/3Nb2/3)O3 ceramics

In this paper, Ba(Mg_1/3Nb_2/3)O₃ (BMN) ceramics with x (x = 0–9) wt% BaWO₄ were synthesized using the conventional solid-state sintering technique. Effects of BaWO₄ addition on the microstructure and microwave dielectric properties of BMN ceramics were evaluated. X-ray diffraction (XRD) analysis showed that there were three phases: main crystalline phase Ba(Mg_1/3Nb_2/3)O₃ and secondary phases BaWO₄ and Ba₅Nb₄O₁₅. Meanwhile, the (100) super-lattice reflection peaks shifted to a higher 2θ angle with increasing BaWO₄ content. SEM photographs suggested that BaWO₄ working as a sintering additive promoted the densification and grain growth. The dielectric properties were examined by Vector network analyzer. The dielectric constant (ε_r) was largely determined by the relative density and phase composition. Meanwhile, the addition of BaWO₄ had a positive effect on the Q × f value, for example the specimen with x = 5 possessed the highest Q × f value of 111,300 GHz. Optimum microwave dielectric properties (ε_r = 31.7, Q × f = 111,300 GHz (f = 8 GHz) and τ_f = 0.16 ppm/°C) were obtained for the specimen with x = 5 sintered at 1350 °C for 6 h.