Effect of MgO doping on electrical characteristics of ZnO–0.5 mol% V2O5–2 mol% MnO varistors

Abstract

Most of commercial ZnO varistors containing Bi2O3 exhibit excellent properties but they have few drawbacks due to Bi2O3 having high volatility, high reactivity, and high sintering temperature. In this study, V2O5 is added as the varistor forming oxide to lower down the sintering temperature of ZnO varistors. It was found that addition of V2O5 to ZnO leads to lower down the sintering temperature to 600 °C. However, the addition of V2O5 has no improvement in the electrical characteristics, and they need many additives to obtain high performance. For that, the non-linear properties in these varistors can be improved by incorporation of some oxide additives. The MnO and MgO were used as minor oxide additives. The effect of MgO (0–1 mol%) on the microstructure and electrical properties have been studied in ZnO–0.5 mol%–V2O5–2 mol% MnO system. The phase composition of samples consists mainly ZnO grains, while Zn3(VO4)2 and ZnV2O4 are the secondary phases. MgO is found to be effective as a grain growth inhibitor, and MnO is founded to be an electrical performance enhancer. Better varistor performance has been achieved for 97.4 mol% ZnO, 0.5 mol% V2O5, 2.0 mol% MnO and 0.1 mol% MgO with non-linear coefficient α = 16, breakdown voltage 251.3 V/mm and leakage current JL = 7.7 × 10−5 A/cm2. SEM morphology shows the average grain size depends on Mg and Mn content.