The role of oxide optimization in improving the electrical properties of ZnO varistors

Zinc oxide-based varistors are nonlinear voltage-dependent ceramic resistors used to suppress and limit transient voltage surges. However, due to their structural inhomogeneity, current concentration may come into existence, which causes thermal stress in local areas that even may destroy the components. As a result, these elements lose their reliability and ability to protect. In this study, the effect of structural inhomogeneity on their electrical properties was analyzed and demonstrated. This analysis contributes to a deeper understanding of the impact of structural inhomogeneity on their performance in terms of surge energy absorption capability. In addition, to make a technological contribution, experiments using the classical proceeding were carried out to identify the optimal proportions for the following oxides (Bi2O3, Nb2O5, MnO2, Co3O4, Cr2O3, NiO, Ce2O3, La2O3). Using the optimal proportions of the oxides, a new ZnO varistor was manufactured. Characterization of the manufactured new varistor showed that it has a low inhomogeneity factor β = 0.11 and a high nonlinear coefficient α = 100 ± 1. This demonstrates that the manufactured varistor has a reasonable structural homogeneity, which allows for a uniform distribution of the current passing through it. For further evidence, the new varistor was shocked by 8/20 μs regular high pulses with a current of 15KA and a voltage of 3 kV for each pulse. No puncture failure was observed, which indicates its ability to absorb excess voltage.