Effects of MnO2 and WO3 co-doping and sintering temperature on microstructure, microwave dielectric properties of Ba2Ti9O20 microwave ceramics

Ba2Ti9O20 (short for B2T9) ceramics doped with 0.9 mol% MnO2 and y mol% WO3 were prepared by solid-state reaction. The influence of sintering temperature, content of WO3 dopant and the molar ratio x of TiO2: BaCO3 on crystal structure, microstructures as well as microwave dielectric properties of B2T9 ceramics was systematically investigated. The major phase of all samples is B2T9, and the minor phase is BaWO4, respectively. The content of impurity TiO2 alternates with the variation of compositions and sintering temperature, which also leads to different microwave dielectric properties. With the continuous increase of the sintering temperature, the B2T9 phase grains gradually grow larger and transform from rod grains to plate-like grains. The enlargement and flattening of grains also result in the decrease of compactness and deterioration of microwave dielectric properties. It is found that B2T9 ceramics possess better performance when the sintering temperature is 1340°C, which is related to lower TiO2 content, BaWO4, B2T9 grain size, aspect ratio of B2T9 phase and high compactness. When x = 4 and y = 0.2, the relative dielectric constant, quality factor and the temperature coefficient of resonant frequency are 38, 23758 and 7 ppm/°C, respectively.