Effect of Ba Addition on Grain Growth of ZnO and Electrical Characteristics of Bi-based ZnO Varistors

With the goal of fabricating low-breakdown-voltage (varistor voltage) varistors, the effect of adding Ba to Bi-Co-Mn-added ZnO varistors on the ZnO grain size was investigated. In order to make the grain size of a ZnO uniform, calcined additives were mixed with ZnO powder to form the uniform liquid phase of Ba and Bi considering that grain growth of ZnO could be markedly promoted by adding both Ba and Bi. Furthermore, in order to make the grain size of a ZnO uniform without making small the grain size, small amount of Sb as an additive was added. ZnO grain size became large and both the nonlinearity index of voltage-current characteristics and varistor voltage increased with increasing calcination temperature of additives. However, the improvement of the tolerance characteristics to the electrical degradation was not found. Addition of small amount of Sb such as 0.01 mol% is effective in suppressing the deviation of the grain size of ZnO without making small the grain size and improved the tolerance characteristics to the electrical degradation, because the compound of Ba and Mn was not formed.