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The novel CuO-doped dense tin oxide varistor ceramics are investigated. The densification of tin oxide varistor ceramics could be greatly improved by doping copper oxide additives. The introduction of antimony additives into a SnO2.CuO ceramic system would make it possess excellent nonlinearity. The sample doped with 0.05 mol% Sb2O3 possesses the highest nonlinearity coefficient (α = 17.9) and the lowest leakage current density (JL = 52 μA cm−2) among all the samples. A modified defect barrier model is introduced to explain the formation of the grain-boundary barrier. The nonlinear behaviour of (Cu, Sb)-doped SnO2 varistor system could be explained by the barrier model.

We have found a new composite SnO2?Zn2SnO4 varistor material and the effect of different content ratios of SnO2 to Zn2SnO4 on this system is investigated. The lowest breakdown voltage (EB = 6.4?V/mm) and the highest relative dielectric constant (?r = 1.54?104) with higher nonlinear coefficient (? = 4.5) is obtained when the ratio of SnO2 to ZnO equals 100/35. The disappear of the Zn2SnO4 peak in x-ray diffraction (XRD) spectra of the SnO2+2.5?mol%ZnO sample and the electric insulation behaviour of the samples with 2.5?mol% ZnO and 200?mol% ZnO indicate that 2.5?mol% ZnO can be dissolved into SnO2 lattices and some reaction contributing to nonlinear electrical behaviour should occur between SnO2 and Zn2SnO4. The role of oxygen on the grain boundary is confirmed by the degradation of nonlinear electrical properties and the increase of relative dielectric constant of the samples annealed in nitrogen-rich atmosphere.

We investigate the effects of Er2O3 on electrical properties of the SnO2.CoO.Ta2O5 varistor system sintered at 1400 degrees C. It is found that all the samples have excellent nonlinear electrical characteristics and the sample with 0.50 mol% Er2O3 has the best nonlinear electrical property and the highest nonlinear coefficient (α = 43.7). The high nonlinear coefficient value obtained in the system indicates that the SnO2-based varistor is a candidate for ZnO-based varistors in commercial applications. Er2O3 additive can significantly affect the average grain size. With increasing Er2O3 concentration from 0.10 mol% to 1.00 mol%, the average grain size decreases from 21.2 μm to 10.6 μm, the breakdown electrical field increases from 208 V/mm to 459 V/mm, and the relative electrical permittivity decreases from 2440 to 1210. The reason that the grain size decreases with increasing Er2O3 concentration is explained. Also, we present a modified defect barrier model to illustrate the grain-boundary barrier formation of Er2O3-doped SnO2 based varistors.