Impact of calcination on low-temperature sintered Bi2O3 varistors: varistor properties and surge current absorption

This study investigated the effects of calcination on the densification, microstructure, varistor properties, and surge current absorption capability of low-temperature sintered ZnO-Bi2O3-Sb2O3-Co3O4-Mn3O4-Nb2O5 varistors. The ZnO, Co3O4, and Mn3O4 were premixed and calcined at various temperatures to reduce grain resistance and improve surge absorption capacity.Calcination at 600°C and 800°C, compared to 1000°C and no calcination, enhanced the surge absorption capacity, attributed to reduced grain resistivity. The introduction of trivalent Co and Mn in place of Zn2+ ions, notably in the 600°C-calcined samples, increased donor concentration and reduced grain resistivity. Conversely, the 1000°C-calcined samples exhibited higher Schottky barriers and lower leakage currents due to increased adsorbed oxygen interacting with Co2+ and Mn2+ ions.