Cr₂O₃ doping in ZnO-0.5 mol% V₂O₅ varistor ceramics

The effects of the amount of Cr₂O₃ (0.5-4 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 ZnCr₂O₄ and α-Zn₃(VO₄)₂ as the minority secondary phases. The addition of Cr₂O₃ is found to be effective in controlling the abnormal ZnO grain growth often found in V₂O₅-doped ZnO ceramic system, and a more uniform microstructure can be obtained. The varistor performance is also improved as observed from the increase in the non-linear coefficient α of the Cr₂O₃-doped ZnO-V₂O₅ samples. The α value is found to increase with the amount of Cr₂O₃ for up to 3 mol% Cr₂O₃ content. Further increase in Cr₂O₃ is found to cause a decrease in the α value. The highest α value of 28.9 is obtained for the ZnO-0.5 mol% V₂O₅-3 mol% Cr₂O₃ sample.