Dependence of La2O3 content on the nonlinear electrical behaviour of ZnO, CoO and Ta2O5 doped SnO2 varistors

The effects of La₂O₃ on the properties of (Zn, Co, Ta) doped SnO₂ varistors were investigated in this study. The samples with different La₂O₃ concentrations were sintered at 1400 °C for 2 h and their properties were characterized by XRD, SEM, I-V and impedance spectroscopy. The grain size was found to decrease from 13 μm to 9 μm with increasing La₂O₃ content. The addition of rare earth element leads to increase the nonlinear coefficient and the breakdown voltage. The enhancement was expected to arise from the possible segregation of lanthanide ion due to its larger ionic radius to the grain boundaries, thereby modifying its electrical characteristics. Furthermore, the dopants such as La may help in the adsorption of O′ to O″ at the grain boundaries characteristics.