The influence of CaO doping on the microstructure and electrical properties of ZnO-based varistor ceramics

The present investigation examines the influence of Ca-doping on the microstructural characteristics and electrical properties of two distinct varistor systems: ZnO-Cr2O3-based ceramics and the ZnO-Bi2O3 system. Incorporating CaO in ZnO-Cr2O3-based varistor ceramics was seen to augment diffusion mechanisms, resulting in amplified grain enlargement and a broader spectrum of breakdown voltages. Concurrently, the introduction of Ca-doping has been seen to elevate the electrostatic Schottky barrier, leading to an increase in the nonlinear coefficient and a decrease in the leakage current. This finding holds considerable importance for utilizing overvoltage protection in diverse voltage ranges [1]. On the other hand, within the ZnO-Bi2O3 system, the introduction of CaO doping resulted in a drop in crystallite size, alterations in phase composition, an increase in density, and a reduction in grain size. An optimal breakdown field was seen at a particular concentration of CaO, as shown by impedance spectroscopy, which detected several relaxations associated with the production of defects. The results above enhance our comprehension of the impacts of Ca-doping on various varistor systems and provide significant insights into their prospective uses [2].