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.