High Voltage Gradient ZnO-Based Varistors from ZnO Nano-powders for DC Current Switching Application

With the increasing demand for high voltage level and miniaturization of extensive power equipment, ZnO ceramics, as key energy absorption elements in DC current breakers, are required to possess even higher voltage gradient. In this paper, nano-sized starting materials ZnO powders were employed to achieve the high voltage gradient. The effect of sintering temperature on the microstructural evolution and electrical characteristics of these obtained varistors were investigated by means of XRD, SEM, J-E measurement and dielectric spectroscopy. Experimental results showed that the fine sized powder could contribute to the high voltage gradient; the optimized sintering temperature for nano-sized starting ZnO powders was 1050°C. The obtained ZnO ceramics sintered at 1050°C exhibited high voltage gradient of 805 V/mm, which was over 4-times than that of the commercial varistors. Meanwhile such ceramics possessed large nonlinear coefficient of 30 and the low leakage current of 1.38 μA/cm2. Such improved performance may could be ascribed to the decreased grain size, the enhanced microstructure homogeneity and the well-formed double Schottky-barrier. Such result indicated the nano-sized ZnO powders as the starting raw material may benefit the high performance of ZnO varistors and is a promising solution to the miniaturization of DC current breakers.