The influences of bismuth antimony additives and cobalt manganese dopants on the electrical properties of ZnO-based varistors

This paper investigates the influences of additive contents and the additive ratio to dopants on the electrical characteristics of ZnO-based varistors. Bismuth and antimony are chosen as the additives while cobalt and manganese are selected as the dopants in this study. Our previous works discussed the influences of the initial additive content on the electrical characteristics of ZnO-based varistors without considering the dopant content and the weight loss during processing and sintering. Therefore, in this study, we fabricated varistors with same initial formula after sintering for 1, 3 and 5 h, respectively. The sintering temperatures were 950 and 1100 °C. After sintering, the additive content and dopant content of the varistors were measured using an inductively coupled plasma-atomic emission spectrometer (ICP). The experimental results showed that when the additive-content varies from 1.44 to 3.59 at % and the dopant/additive ratio changes from 0.16 to 0.69, the nonlinear coefficient, α, reaches up to 48 and the breakdown field Ebk is to 895 V mm−1. The average grain size is 2.7 μm. The α value is higher with the higher additive-content and the lower dopant/additive ratio and vice versa. The breakdown field Ebk is increased with the additive-content increasing and sintering temperature lowering at a given dopant-content. The grain size is increased with the increase in sintering temperature while the bismuth concentration decreased. The observed effects are related to the quality of grain boundaries and the conductivity of grains.