Fabrication of Bismuth-based Zinc Oxide Varistors with High Varistor Voltage by Addition of Tin and Yttrium Oxides

The effects of the addition of tin oxide (SnO2) and yttrium oxide (Y2O3) to bismuth (Bi)-manganese (Mn)-cobalt (Co)-silicon (Si)-chromium (Cr)-nickel (Ni)-added zinc oxide (ZnO) varistors (a basic varistor) on the varistor voltage, resistance to electrical degradation, and leakage current were investigated. The addition of SnO2 increased both the varistor voltage and the resistance to electrical degradation. However, simultaneous addition of both SnO2 and Y2O3 increased the varistor voltage but the resistance to electrical degradation deteriorated. ZnO varistors with varistor voltage over approximately 520 V/mm, excellent resistance to electrical degradation, and low leakage current could be obtained by adding SnO2 with SnO2-to-ZnO molar ratio of approximately 1:10 to the basic varistor.