Effects of Cr2O3 on the properties of (Co, Nb)-doped SnO2 varistors

The effects of Cr2O3 on the properties of (Co, Nb)-doped SnO2 varistors were investigated. The samples with different Cr2O3 concentrations were sintered at 1350 degreesC for an hour. The properties of (Cr, Co, Nb)-doped SnO2 varistors were evaluated by determining their I-V and epsilon-f relations, measuring their resistivities, scanning electron microscopy. It was found that the breakdown electrical field increases from 400 to 1000 V mm(-1) and relative electrical permittivity decreases from 2022 to 147 with increasing Cr2O3 from 0.00 to 0.07 mol%. Nonlinear coefficient presents a peak of alpha = 52 and grain boundary barrier becomes highest when 0.06 mol% Cr2O3 was added. Electrical permittivity and grain size decreases with increasing the content of Cr2O3. In order to illustrate the grain boundary barrier formation in this varistor system, an interface defect model was introduced. (C) 2002 Elsevier Science B.V. All rights reserved.