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

Abstract The microstructure and electrical properties of ZnO Bi 2 O 3 –MnO 2 -based varistor ceramics doped with different Cr 2 O 3 content were investigated. The addition of Cr 2 O 3 caused a transformation of minor secondary phases from Bi 7.72 Mn 0.28 O 12.14 to Bi 2 O 3 dissolving different amount of Cr. The average grain size of sample with 0.2 mol% Cr 2 O 3 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 Cr 2 O 3 , 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 Cr 2 O 3 promote the grain-growth at a relatively low sintering temperature, and thus result in the shift of breakdown voltages to a lower value.