Improvement in the non-linear electrical characteristics of the SnO2·CoO·Ta2O5 varistor material with La2O3 additive

The effect of La2O3 additive on a SnO2-based varistor material sintered at 1350 °C for 80 min was investigated. It was found that La2O3 significantly decreases the grain size and improves the non-linear electrical properties of SnO2-based varistors. The sample with 1.00 mol% La2O3 has the best non-linear electrical property and the highest non-linear coefficient (α = 23.0) among all the samples. The reason that the grain size decreases with increasing La2O3 concentration is explained. The permittivity decrease with increasing La2O3 concentration is caused by the ratio of grain size to barrier width. A modified defect barrier model was introduced in which the negatively charged acceptors substituting for Sn ions should be located at the grain boundaries.