Effects of SiO₂ and B₂O₃ on electrical properties of low-temperature sintered ZnO–Bi₂O₃ varistors

This study utilized a conventional solid-state reaction method to prepare ZnO–Bi₂O₃–Sb₂O₃–Co₃O₄–Mn₃O₄–Nb₂O₅ varistors sintered at low temperatures of 860 °C–880 °C. The effects of the different amounts of SiO₂ and SiO₂-B₂O₃ co-doping on the microstructure and varistor properties were investigated. The nonlinearity coefficient (α) increased from 51 for the sample without adding SiO₂ to 66 for the sample with 1.0wt% SiO₂, and the breakdown voltage increased from 834 to 1260 V/mm. However, with excess SiO₂ addition, the α value gradually decreased from 66 for the sample with 1 wt% SiO₂ to 52 for the sample with 2.0 wt% SiO₂, while the breakdown voltage continued to increase. Co-doping SiO₂–B₂O₃ improves liquid phase sintering due to the relatively low melting point of SiO₂–B₂O₃–Bi₂O₃ additives. The α value increased from 66 for the sample without adding B₂O₃ to 83 for the sample with 2.0 wt% B₂O₃, while the breakdown voltage decreased from 1260 to 1120 V/mm. In comparison to higher temperature alternatives, the lower sintering temperatures (860 °C–880 °C) used in this study result in lower energy consumption during the manufacturing process. Because of their favorable cost-energy efficiency ratio, the SiO₂–B₂O₃ co-doped ZnO–Bi₂O₃ varistors emerge as promising candidates for large-scale production.