Abstract
The effect of both Mn and Co addition on the electrical degradation of ZnO varistors were investigated based on voltage-current (V-I) characteristics, capacitance-voltage (C-V) characteristics, isothermal capacitance spectroscopy (ICTS), and X-ray diffraction (XRD). The optimum Co content to prevent the electrical degradation is approximately 0.5mol% for Bi-Mn(0.5)-Co-added ZnO varistors. Correlation of the improvement of the electrical degradation with the structure changes of ZnO varistor by Mn and Co addition was investigated by XRD. It is found that the crystal structure of α-Bi2O3 in the grain boundary changed to Bi7.65Zn0.35O11.38 for Bi-Mn-Co(0.5mol%) added samples. It is suggested that these structure changes of varistors with Mn and Co addition contribute to the improvement of the electrical degradation characteristics of Bi-Mn-Co-added ZnO varistors.
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