Effect of Mn2(+) on the electrical nonlinearity of (Ni, Nb)-doped SnO2 varistors

The reason that the (Ni, Nb)-doped SnO2 varistors exhibit poorer densificat ion and electrical nonlinearity than the (Co, Nb)doped SnO2 varistors is ex plained. The effect of Mn2+ on the electrical nonlinear properties of SnO2 based ceramics were investigated. The sample doped with 0.10 mol% MnCO3 exh ibits the highest reference electrical field of 686.89 V/mm, the highest el ectrical nonlinear coefficient of 12.9, which is consistent with the highes t grain-boundary defect barriers. It can be explained by the effect of the substitution of Sn4+ for Mn2+, which facilitate the formation of the defect barriers, and the maximum of the substitution, The shrinkage rates increas e with the doping of MnCO3, although the sample doped with 0.5 mol% MnCO3 a ppears the highest density (rho = 6.87 g/cm(3)). In order to illustrate the grain boundary barriers formation in SnO2.Ni2O3.Nb2O5.MnCO3 varistors, a g rain-boundary defect barrier model was introduced. (C) 2001 Elsevier Scienc e Ltd and Techna S.r.l. All rights reserved.