Effects of MgO doping in ZnO–0.5 mol% V2O5 varistors

The effects of MgO (0–40 mol%) on the microstructure and the electrical properties have been studied in a binary ZnO–0.5 mol% V₂O₅ system. The microstructure of the samples consists mainly of ZnO grains with MgO and γ-Zn₃(VO₄)₂ as the minority secondary phases. MgO is found to be effective as a grain growth inhibitor in controlling the ZnO grain growth, and a more uniform microstructure can be obtained. The non-linear coefficient α value is found to increase with the amount of MgO, and a highest value of 8.7 is obtained for the sample doped with 10 mol% MgO. Further addition of ≥20 mol% MgO decreases the α value.