Microstructure and current-voltage characteristics of multicomponent vanadium-doped zinc oxide varistors

The effects of the oxide additives MnO2, Co3O4, and Sb2O3, commonly incorporated in commercial Bi2O3-doped ZnO varistors, on the current-voltage characteristics and microstructure of 0.25 mol% V2O5-doped ZnO varistors have been studied. MnO2 is the most significant additive in terms of its effects on varistor performance. Varistor performance can also be improved by increasing the V2O5 content to 0.5 mol% in a ZnO ceramic containing 1 mol% MnO2. Further increases in the V2O5 content of 1 mol% MnO2-doped material cause a deterioration in varistor behavior. The microstructure of the samples consists mainly of ZnO grains with zinc vanadates as the minority secondary phases. Additional spinel phase is formed when Sb2O3 is incorporated.