Effect of Oxygen Vacancy on Improving the Properties of ZnO-Bi2O3-Based Varistors

ZnO varistor samples generally have poor preparation repeatability. In this work, ZnO varistor samples A and B with the same preparation technique showed significant differences in properties, and the reasons were explored in detail. Nonlinear coefficient (alpha) values of 42.59 and 72.68, and leakage current density of 0.013 mA/cm(2) and 0.002 mA/cm(2) were found for samples A and B, respectively, which are markedly different between the samples. However, samples A and B showed the same phases. In addition, samples A and B exhibited mean grain size (d) of 2.21 mu m and 2.47 mu m, double Schottky barrier height (phi(B)) of 0.45 eV and 0.48 eV, and grain boundary resistivity (rho(gb)) of 5.32 x 10(6) Omega m and 5.40 x 10(6) Omega m, respectively, which were all similar between the two samples. According to the low-temperature dielectric spectral analyses, the values of k(1) of samples A and B, reflecting the concentration of interstitial zinc, were 14.06 and 11.09, and the values of k(2) reflecting the concentration of oxygen vacancy were 7.48 and 3.35, respectively. Therefore, the obvious difference in the electrical properties between samples A and B may be caused mainly by the obvious difference in the concentration of oxygen vacancy. Thus, this work provides evidence of the effects of oxygen vacancy on the electrical properties of ZnO varistors.