Abstract
ZnO varistors of the excellent tolerance characteristics of electrical degradation were made by adding Bi2O3-MnO2-Co3O4-Cr2O3-SiO2-Sb2O3-NiO in them. The tolerance characteristics of electrical degradation were evaluated by changing amount of ZrO2. The evaluation methods are voltage-current (V-I) characteristics, X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion X-ray spectroscopy (EDX). Monoclinic, tetragonal ZrO2 and the compounds originated from Zr were observed at both the grain boundaries and triple points. Moreover, The compounds originated from Zr and added Sb improved the tolerance characteristics of electrical degradation. On the other hand, especially monoclinic ZrO2 deteriorated the tolerance characteristics of electrical degradation. It is one factor of the improvements of the tolerance characteristics of electrical degradation that the mobility of oxide ions or interstitial Zn2+ ions might be hidered by forming the compounds contained Zr, Sb, Si, and Bi atoms. The tolerance characteristics of electrical degradation for ZnO varistors added ZrO2 was improved compared with that not-added ZrO2 by heat treatment.
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