Influence of Calcium Element on Microstructure and Electrical Properties of ZnO Varistor with Lesser Dopants

Abstract

AbstractIn this paper, the influence of Ca‐doping on microstructure and electrical characteristics of ZnO varistor ceramics is studied. With the increase of the doping concentration of calcium, the ZnO ceramics show strong directional growth along the Ca2MnO3.5 phase and the intensity of the X‐ray diffraction peaks of the Ca2MnO3.5 phase increase obviously, which indicates that the phase structure of ZnO ceramics is significantly affected by the calcium concentration. The average grain size of 0, 1, 2, and 3 mol% Ca‐doped ZnO ceramics is 7.2, 5.2, 4.8, and 4.2 µm, respectively, confirming the doping of Ca restrained the growth of grain in ceramics. The varistor ceramics doped with 1 mol% Ca have a density of 4.37 g cm−3, with a nonlinear coefficient of ∼41 at room temperature. They can be used to protect the electrical circuits from over voltages in the range of 280–460 V. Moreover, the ZnO ceramics show good temperature stability and the nonlinear coefficient changes slightly when the temperature changes from 25 to 150 °C; especially for varistor ceramics with 2 mol% Ca, the nonlinear coefficient is stable at about 37.