The characteristics of ZnO–Bi2O3-based varistor ceramics doped with Y2O3 and varying amounts of Sb2O3

ZnO–Bi2O3-based varistor samples doped with 0.45 mol% of Y2O3 and varying amounts of Sb2O3 in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb2O3 did doping with Y2O3 resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y2O3-containing phase) at the grain boundaries, which very effectively hinders the grain growth. Despite of a decrease in the amount of added Sb2O3 from 1.8 to 0.45 mol% and a significant decrease in the amount of spinel phase the samples had a similar ZnO grain size and a threshold voltage of 200 V/mm. The results confirmed that doping with Y2O3 is a very promising route for the production of fine-grained high-voltage ZnO–Bi2O3-based varistor ceramics, and determining the proper amounts of added Sb2O3 and Y2O3 is of great importance.