Influence of Y2O3 on electrical properties and dielectric characteristics in ZnO based varistor ceramics

The voltage gradient of ZnO based varistor is usually opposite to the average grain size. It has been reported that the growth of ZnO grains could be inhibited by doping with rare-earth oxides. In this paper the electrical properties and dielectric characteristics of ZnO based varistor ceramics with various Y₂O₃ additions are investigated. The voltage gradient of varistor samples markedly increase with Y₂O₃ contents increasing. However, the leakage currents and nonlinear coefficients of the samples are deteriorated at the same time. Measurement results show the dielectric constant and dissipation factor of varistors are affected by the doping ratio of yttrium oxide, and the decrement of dielectric constant as the Y₂O₃ addition increasing could be attributed to the internal boundary layer capacitance (IBLC) effect. Meanwhile, the relaxation peak of dissipation factor shifting to lower frequency may be related to the variation of intrinsic defects in ZnO grains.