Effects of Sb2O3 on the microstructure and electrical properties of ZnO–Bi2O3-based varistor ceramics fabricated by two-step solid-state reaction route

Abstract In this work, the ZnO–Bi2O3–Cr2O3–Co2O3–MnO2 varistors doped with different content of Sb2O3 were prepared by two-step solid-state reaction route, including a pre-calcining of the mixtures of nanosized ZnO and the other additives at an optimized temperature, followed by a consequent sintering process at different temperatures. Meanwhile, the effects of Sb2O3 on the sintering temperature, microstructure and electrical properties of the objective varistors were investigated. It was found the densification temperature went up in a proper range and the content of pyrochlore phase, spinel phase and β-Bi2O3 phase increased with the increasing content of Sb2O3, while the grain size of ZnO–Bi2O3-based varistor reduced. The results demonstrated that at the same sintering temperature, the second particles increased with the increasing amount of Sb2O3, which was helpful to control the grain growth, leading to a higher breakdown voltage. However, the decrease of α-Bi2O3 phase (melting point of α-Bi2O3 phase is 825 °C), which is the main component of the liquid Bi2O3 phase in the sample during sintering process, leads to the increase of the sintering temperature of the green pallet. As a result, the ZnO varistor doped with 3.0 mol% Sb2O3 sintered at 1000 °C exhibited the highest breakdown voltage of 1863.3 V/mm. By contrast, the ZnO varistor without Sb2O3 doping sintered at 900 °C had the optimum nonlinear coefficient of 59.8.