Influence of Sintering Temperature and ZrO₂ Dopants on the Microstructure and Electrical Properties of Zinc Oxide Varistors

Abstract

This paper investigated the effects of sintering temperature on the microstructure and electrical properties of ZrO2-doped zinc oxide (ZnO) varistor ceramics. The results show that, the additive ZrO2 exists as independent second phase between ZnO grains, which can limit the growth of ZnO grains and improve the voltage gradient. With the increasing of ZrO2, the content of extrinsic elements (Mn, Sb, Co, Cr) in the grain boundary layers tends to increase first and then decease. When ZrO2 content is more than 1.0mol%, the electrical performance of ZnO varistors decreases sharply. With the increasing of sintering temperature, the ZnO grain size increases and the voltage gradient decreases. When the sintering temperature is larger than 1200°C, more monoclinic ZrO2 phase transformed into cubic phase, and more micropores are generated, causing the non-linear coefficient to decrease and the residual voltage ratio and leakage current to increase. With a sintering temperature of 1150°C and a ZrO2 content of 1.0mol%, the ZnO varistors can reach the overall optimum electric performance, exhibiting a breakdown voltage of $E_{\mathrm {1mA}}=420\text{V}$ /mm, a nonlinear coefficient of $\alpha = 58$ , a residual voltage ratio of $C_{\mathrm {R}}= 1.87$ , and a leakage current of $I_{\mathrm {L}}= 4 ~\mu \text{A}$ . The studies in this paper can give reference for the development of high quality ZnO arresters.

Keywords

• Varistors
• temperature control
• ceramics