Low-temperature sintering and microwave dielectric properties of (1 - x)MgTiO₃-xCaTiO₃ ceramics using bismuth addition

The effects of bismuth addition on the microwave dielectric properties of (1 - x)MgTiO₃-xCaTiO₃ ceramics were investigated. MgTiO₃-CaTiO₃ (hereafter referred to as MCT) ceramics was prepared by the conventional solid-state method. With a small amount of Bi₂O₃ addition, the sintering temperature of MCT ceramics can be effectively lowered without degrading the dielectric properties at microwave frequency. At a constant Mg/Ca ratio, the Q × f values are strongly dependent on the amount of Bi₂O₃ addition and decrease with increasing bismuth content owing to the decrease of density, while the ε_r value only shows a small increase. In the (1 - x)MgTiO₃-xCaTiO₃ system, the microwave dielectric properties could be controlled by varying x. At 1250°C, 0.94MgTiO₃-0.06CaTiO₃ ceramics with 0.2 mol% Bi₂O₃ addition gives a dielectric constant ε_r of 22.6, a Q × f value of 53000 (7 GHz) and a τ_f value of -2.9 ppm/°C.