Influence of Cr2O3 on ZnO-Bi2O3-MnO2-based varistor ceramics

The microstructure and electrical properties of ZnO-Bi2O3-MnO2-based varistor ceramics doped with different Cr2O3 content were investigated. The addition of Cr2O3 caused a transformation of minor secondary phases from Bi7-72Mn0.28O12.14 to Bi2O3 dissolving different amount of Cr. The average grain size of sample with 0.2 mol% Cr2O3 increased remarkably froth a range of 6.38-6.62 mu m to 9.79 mu m, and the barrier voltage decreased to 1.31 V. With the increase of Cr2O3, the nonlinear coefficients of sintered samples decreased to 25.0 at 0.2 mol%, and then it further increased up to 40.0, a comparable value with the one of the undoped sample, at 0.8 mol%. The results showed small amounts of Cr2O3 promote the grain-growth at a relatively low sintering temperature, and thus result in the shift of breakdown voltages to a lower value. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.