Abstract
ZnO varistor ceramics with a high potential gradient, as well as a high nonlinear coefficient, were reported and analyzed in this paper. With the use of nano-sized ZnO powders, the average grain size was reduced to about 2.6 μm, which successfully raised the potential gradient to 1172 V/mm. Moreover, the nonlinear coefficient increased to 48, and the leakage current was decreased to 8.4 μA/cm2 by doping a moderate amount of MnO (0.9 mol%). This was proven to be caused by the high Schottky barrier height formed at the grain boundary, where the Mn element segregated and, consequently, led to the increased density of interface states. Therefore, this could be considered as a potential method to simultaneously enhance the potential gradient and the nonlinear coefficient of ZnO varistor ceramics.
Highlights
ZnO varistor ceramics are widely employed to protect electrical power systems and electronic devices from surges and overvoltage due to their excellent nonlinear current
The potential gradient (E1mA ) of ZnO varistor ceramics is proportional to the number of grain boundaries (GB) per unit length and the breakdown voltage of a single GB, which is approximately constant at ~3 V [1]
The effects of MnO doping (0.3–1.2 mol%) on the electrical properties of ZnO varistor ceramics prepared by nano sized ZnO powers are inconclusive
Summary
ZnO varistor ceramics are widely employed to protect electrical power systems and electronic devices from surges and overvoltage due to their excellent nonlinear current–. High-performance ZnO varistor ceramics with a high potential gradient, high nonlinear coefficient and low leakage current are urgently required due to the increasing requirements in the fields of device miniaturization, ultra-high-voltage power systems, high-speed electrified railways, and integrated circuits, etc. The commonly accepted approach to enhance the potential gradient is to reduce the grain size, which is generally achieved by optimizing doping [4,8,9,10], sintering [11,12,13] and nano-sized raw materials [5,14,15,16,17,18,19] Among these methods, the most effective method is using nano-sized ZnO powders to prepare ZnO varistor ceramics. The effects of MnO doping (0.3–1.2 mol%) on the electrical properties of ZnO varistor ceramics prepared by nano sized ZnO powers are inconclusive
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