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.