Microstructure and Nonlinear Properties of Microwave‐Sintered ZnO‐V 2 O 5 Varistors: I, Effect of V 2 O 5 Doping

The modification of the densification behavior and the grain‐growth characteristics of the microwave‐sintered ZnO materials, caused by the incorporation of V 2 O 5 additives, have been systematically studied. Generally, the addition of V 2 O 5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 µm can be attained for a sintering temperature as low as 800°C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO‐V 2 O 5 materials but it does monotonously increase their grain size. Varying the proportion of V 2 O 5 in the range of 0.2‐1.0 mol% does not pronouncedly modify such behavior. The leakage current density ( J L ) of these high‐density and uniform‐granular‐structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn 3 O 4 in the ZnO materials, in addition to 0.5 mol% of the V 2 O 5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (α= 23.5) and a low leakage current density ( J L = 2.4 10 ‐6 A/cm 2 ).