Effects of Pr 2O 3 on the nonlinear electrical characteristics and dielectric properties of SnO 2·Co 2O 3·Ta 2O 5 varistor systems

Abstract

The effects of Pr 2O 3 on the SnO 2·Co 2O 3·Ta 2O 5 varistor system sintered at 1300 °C for 80 min were investigated. It is found that Pr 2O 3 affects the grain size, electrical properties and the dielectric properties of the SnO 2-based varistors. The average grain size decreases from 9.4 to 5.6 μm, the breakdown electrical field increases from 2460 to 11,346 V/cm, relative dielectric constant (at 1 kHz) falls from 1988 to 290 and the resistivity (at 1 kHz) rises from 39.3 to 178.3 kΩ cm with an increase in Pr 2O 3 concentration from 0.00 to 1.00 mol%. The sample with 0.10 mol% Pr 2O 3 has the best nonlinear electrical property and the highest nonlinear coefficient ( α=23.9) among all samples. The reason that the grain size decreases with increasing Pr 2O 3 concentration is explained. A modified defect barrier model is introduced to illustrate the grain-boundary barrier formation of Pr 2O 3-doped SnO 2-based varistors.