Densification, microstructural evolution, and dielectric properties of hexagonal Ba(Ti1−xMnx)O3 ceramics sintered with fluxes

Recently, doped hexagonal BaTiO₃ (6h-BaTiO₃) ceramics have been reported as potential candidates used in microwave dielectric resonators. However, similar to other common microwave ceramics, doped 6h-BaTiO₃ ceramics require a high sintering temperature, greater than 1300 °C. In this study, the effect of sintering aids, including Bi₂O₃, B₂O₃, BaSiO₃, Li₂CO₃, CuO, V₂O₅, 5ZnO·2B₂O₃, and 5ZnO·2SiO₂, on the densification, microstructural evolution, and microwave properties of the 6h-Ba(Ti_0.85Mn_0.15)O₃ ceramics was examined. Results indicate that among the fluxes studied, Bi₂O₃, B₂O₃, and Li₂CO₃ could effectively reduce the sintering temperature of 6h-Ba(Ti_0.85Mn_0.15)O₃ ceramics through liquid phase sintering, while retaining the hexagonal structure and the microwave dielectric properties. The best results were obtained for the 6h-Ba(Ti_0.85Mn_0.15)O₃ with the additions of 5 wt% Bi₂O₃ sintered at 900 °C (_r: 54.7, Qf_r: 1323, and τ_f:183.3 ppm/°C), 10 wt% B₂O₃ sintered at 1100 °C (_r: 54.4, Qf_r: 3448, and τ_f: 254.5 ppm/°C), and 5 wt% Li₂CO₃ sintered at 950 °C (_r: 43.7, Qf_r: 2501, and τ_f: −29.8 ppm/°C).