Effect of high-energy mechanical activation on the microstructure and electrical properties of ZnO-based varistors

Zinc oxide-based varistors were prepared by subjecting the mixed oxide powders to high-energy mechanical activation for 5 h and 10 h, respectively. The crystallite sizes of the constituent oxides were refined to 10∼15 nm by 5 h of high-energy mechanical activation. Similarly, the average particle size was refined from 0.45 μm to about 0.18 μm. The material derived from high-energy mechanical activation exhibit a higher density (>98% relative density) and more refined microstructure upon sintering at 1100°C than those of the material derived from the powder subjected to no high-energy mechanical activation. They demonstrate much higher α-values than those of the materials sintered from the oxide powder without high-energy mechanical activation. These enhanced electric properties are due to great structural homogeneity and refined grain size brought about by high-energy mechanical activation.