Effect of Cr2O3 on properties of ZnO-Bi2O3 based high-voltage varistor ceramics

ZnO-Bi2O3-Co2O3-NiO-Mn3O4-SiO2-Cr2O3 varistor ceramics were prepared by solid-phase sintering method.The effects of different doping amounts of Cr2O3 on the microstructure and electrical properties of ZnO varistor ceramics were investigated, and the phases, microstructures and electrical properties of samples were characterized. The results indicate that the addition of Cr2O3 effectively inhibits the abnormal growth of ZnO grains, enhances the uniformity of grain distribution, reduces the ZnO grain resistance and increases the grain boundary resistance.In the range of 0%-0.21% (molar fraction, the same below) of Cr2O3 addition, the nonlinear coefficient of the varistor ceramics increases first and then decreases as the addition amount increases. When the Cr2O3 doping amount is 0.14%, the ZnO varistor ceramics exhibit excellent electrical properties, with a potential gradient E1 mA=216 V·mm-1, leakage current JL=0.36 μA·cm-2, nonlinear coefficient α=25, residual voltage ratio K=1.815, and aging coefficient Kct=0.647. In addition, the initial U1 mA value of varistor ceramics still maintains 96.75% after impacted by 100 kA pulse current twice with 4/10 μs waveform. The Cr2O3 doped ZnO varistor ceramics demonstrate excellent impulse stability and significant application potential for lightning arresters of power distribution systems.