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

The nonlinear electrical properties of TiO2-Y2O4-Nb2O5 ceramics were invest igated as a new varistor material. It was found that an optimal doping comp osition 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 relat ive dielectric constant of 7.6 x 10(4), which is consistent with the highes t and narrowest grain boundary barriers in the composition. Samples doped w ith 0.10 mol.% Nb2O5 exhibit the highest permittivitty and resistivity at l ow frequencies and comparatively lower values at high frequencies in compar ison with other samples studied. In view of these electrical characteristic s. the ceramics of 99.75%TiO2-0.60%Y2O3-0.10%Nb2O5 is a viable candidate fo r 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.