Nickel or cobalt doped zinc oxide varistors

Zinc oxide containing either Ni or Co dopants in various proportions has been investigated. Only zincite phase was found by XRD analysis. Incorporation of Ni or Co into the ZnO structure resulted in a marked shift in the XRD peaks. Remarkable microstructural uniformity was obtained by the addition of 1 mol-% of either Ni or Co oxides. Densification was achieved through atomic diffusion along grain boundaries. All samples showed non-linear I-V dependence. Ni concentration had a non-monotonic effect on breakdown voltage and the non-linear coefficient decreased with increasing Ni content. In contrast, breakdown voltage and non-linear coefficient increased with increasing CoO content.