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.