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

The microstructure and electrical properties of ZnOsingle bondBi2O3–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 from a range of 6.38–6.62 μm to 9.79 μm, 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.