Abstract
Ceramic varistors in ZnO-SrO system containing CoO and MnO as a third component were prepared, and the effect of these additives on the electrical properties and microstructure of the specimens was investigated. The barrier height and the donor concentration were calculated from the 1/C2-V plot, and the nonlinearity of V-I characteristics was explained by the back-to-back Schottky barrier model. The second component SrO is considered to form trap levels at the interface of ZnO grains. The barrier height increases and the donor concentration decreases with increasing CoO content, and the nonlinear exponent α increases. On the other hand, the addition of MnO only decreases the donor concentration. In this case, however, a small amount of MnO (less than SrO content) is not effective, because of the formation of conductive SrMnO3-x in the vicinity of grain boundaries. SrMnO3-x only suppresses the grain growth.
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