Effects of In₂O₃ and Ta₂O₅ co-doping on microstructure and electrical properties of ZnO low-voltage varistor

In this work, ZnO–Bi₂O₃ based low-voltage varistors were prepared by co-doping of In₂O₃ and Ta₂O₅, which achieved a high nonlinear coefficient with a low breakdown voltage. By exploring the microstructure and electrical performance of the samples, it was found that the samples co-doped with In₂O₃ and Ta₂O₅ have uniform microstructure, and the threshold voltage decreased slightly while the leakage current decreased. The best performance of the varistor was obtained at 0.15 mol% Ta₂O₅ doping with a breakdown voltage of 184 V/mm, a nonlinear coefficient of 32.3 and a leakage current of 0.04 μA. The grain boundary resistance of the varistor increased after the co-doping of In₂O₃ and Ta₂O₅, which was conducive to improving performance stability of the sample. All varistors could be aged, but the parameter change rate of doped varistors was significantly smaller.