Effect of barium oxide on the varistor characteristics of zinc oxide ceramics

Abstract

Zinc oxide (ZnO) varistors can be used as the overvoltage surge protectors in the electronic circuit because of their nonlinear current-voltage (l-V) characteristic. This property can be observed in ZnO containing other additives such as bismuth oxide, barium oxide, etc. In this research, the effects of 0.5 and 1.0 wt% BaO on the phase, microstructure and I-V characteristic of 95 wt% ZnO -5 wt% Bi2O3 were investigated. Furthermore, sintering at 900 ํC and 1000 ํC were compared, especially, on the nonlinear coefficient and microstructure of those compositions. The results from XRD showed that BaO could prevent the evaporation of Bi2O3 acted as an insulating layer of grains. Consequently, a higher nonlinear coefficient was obtained from 95 wt% ZnO-5 wt% Bi2O3 doped with Ba. In addition, BaO increased the grain size of this composition affecting a higher nonlinear coefficient. However, the higher sintering temperature was required to maintain the optimum density of sample. Moreover, the compositions sintered at 1000 ํC provided not only a higher value of the coefficient but also uniform mcrostructure than those sintered at 900 ํC.