Nonlinear electrical properties of TiO2-Y2O3-Nb2O5 capacitor-varistor ceramics

The nonlinear electrical properties of TiO2-Y2O4-Nb2O5 ceramics were investigated as a new varistor material. It was found that an optimal doping composition of 99.75%TiO2-0.60%Y2O5-0.10% Nb2O5 was obtained with low breakdown voltage of 8.8 V mm(-1) high nonlinear constant of 7.0 and ultrahigh relative dielectric constant of 7.6 x 10(4), which is consistent with the highest and narrowest grain boundary barriers in the composition. Samples doped with 0.10 mol.% Nb2O5 exhibit the highest permittivitty and resistivity at low frequencies and comparatively lower values at high frequencies in comparison with other samples studied. In view of these electrical characteristics. the ceramics of 99.75%TiO2-0.60%Y2O3-0.10%Nb2O5 is a viable candidate for capacitor-varistor functional devices. The performance of the ceramics as a function of Nb-doping depends primarily on the extent of substitution of Ti4+ with Nb5+. In order to illustrate the role of grain boundary barriers for high Nb-doping co-concentrations in TiO2-Y2O3-Nb2O5 varistors, a grain-boundary defect barrier model was introduced. (C) 2001 Elsevier Science B.V. All rights reserved.