Influence of Co2O3 doping on the microstructure and electrical properties of ZnO-Bi2O3-based varistors

In this work, the microstructure (for instance grain size and elemental distribution) and comprehensive electrical performances of ZnO-Bi2O3-Cr2O3-MnO2 varistors, with various amounts of Co2O3 prepared via the traditional solid-state sintering method were investigated. The influences of Co2O3 doping on the microstructure of the ZnO varistors were evaluated via X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectrometer (EDS), while the effects on the electrical performance of the ZnO varistors were analyzed via voltage source meter and inductance-capacitance-resistance meter. The experimental results indicate that Co2O3 doping can contribute to improve the electrical characteristics of ZnO varistors. The double Schottky barrier height vb and nonlinearity coefficient alpha was enhanced significantly. Meanwhile, Co2O3 doping can effectively reduce ZnO grain resistivity pg and increase grain boundary resistivity pgb. In this research, there was an optimal content of Co2O3 (0.5 mol%), the alpha of the ZnO varistors reaches the maximum value of 46.7 and the vb reaches the maximum value of 0.63 eV with the optimal content.