Zinc interstitial as a universal microscopic origin for the electrical degradation of ZnO-based varistors under the combined DC and temperature condition

The electrical degradation of four different commercial ZnO-based varistors under the combined DC bias and high temperature condition was investigated with XRD, SEM, I-V, impulse current measurement, and dielectric spectroscopy, respectively. Contrary to the negligible structural changes, the electrical properties vary significantly after the degradation from sample to sample. Those deviations could not be completely ascribed to the differences in fabrication, but instead be consistently explained in terms of the intrinsic defect structure of ZnO ceramics. With a detailed analysis of their dielectric spectra in broad temperature and frequency ranges, it was found that zinc interstitial is the main intrinsic defect species responsible for the observed electrical degradation and its density could be used as a “universal” microscopic parameter to characterize the macroscopic electrical degradation. In addition, depending on the conduction mechanism, the role taken by Zni also differs correspondingly.