Ge-added TiO2-Ta2O5-CaCO3 varistor ceramics

The influence of doping with Ge on the nonlinear coefficient α and the breakdown electric field EB of TiO2-Ta2O5-CaCO3 varistor ceramics was investigated. In this study, TiO2-Ta2O5-CaCO3 varistor ceramics added with Ge was successfully prepared using the traditional method of ball milling-molding-sintering. The electrical performance, including the nonlinear coefficient α, the breakdown electric field EB, and the leakage current JL, are tested using a varistor direct current parameter instrument. The average barrier height ΦB of each sample is calculated using the relevant formula. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electronic microscopy analyses demonstrated that Ge doping notably changed the microstructure of TiO2-Ta2O5-CaCO3 ceramics, thereby increasing α and decreasing EB. When the doping contents of Ta2O5 and CaCO3 were 0.2 and 0.4 mol%, respectively, the optimum doping content of 0.9 mol% Ge exhibited high α (10.2), low EB (14.1 V mm−1), and high ΦB (0.95 eV). These results are superior to previous findings. In addition, Ge as sintering aid reduced the sintering temperature caused by the low melting point. The optimal sintering temperature was 1300 °C for the TiO2-Ta2O5-CaCO3 ceramics doped with Ge.