Effects of Sb addition on ZnO grain growth and the electrical characteristics of Ba-added-Bi-based ZnO varistors

The varistor voltage increases as the number of ZnO grain boundaries between electrodes increases. Therefore, in order to fabricate varistors with low varistor voltages, it is necessary to reduce the number of ZnO grain boundaries between electrodes. The present study uses this method for increasing the ZnO grain size. With the goal of fabricating varistors with low varistor voltages, the effect on the ZnO grain size of adding Sb to Bi- Ba-Co-Mn-added ZnO varistors was investigated. Ba was added in order to increase the ZnO grain size, and Sb was added in order to achieve a uniform ZnO grain size without reducing the grain size. The addition of a small amount of Sb reduced the formation of ZnO grains having a smaller grain size, and the addition of 0.02 mol% Sb to the 0.5-mol%-Bi- and 0.5 mol% Ba added ZnO varistor exhibited a low varistor voltage of approximately 31 V/mm and the highest resistance to electrical degradation, because compounds containing both Ba and Mn do not form at grain boundaries between ZnO grains.