Effects of Ta2O5on the grain size and electrical properties of SnO2-based varistors

The effects of Ta2O5 on SnO2-based varistors were investigated. It was found that Ta2O5 significantly affects the grain size and the electrical properties. The average grain size decreases from 9.3 to 3.8 µm, the breakdown electrical field increases from 246 to 1412 V mm−1 and relative electrical permittivity decreases from 1.9 to 0.42 k with an increase in Ta2O5 concentration from 0.10 to 1.00 mol%. The sample with 1.00 mol% Ta2O5 has the best nonlinear electrical property and the highest nonlinear coefficient (α = 52.6) among all samples. The reason for grain size decrease with increasing Ta2O5 concentration is explained. To illustrate the grain–boundary barrier formation of (Co, Ta)-doped SnO2 varistors, a modified defect barrier model is introduced.