Effect Of High Pressure And Temperature Treatment On The Microstructure And Varistor Properties Of ZnO Nanocrystals

In this paper, the ZnO nanocrystals were processed under high pressure and temperature on a cubic high pressure apparatus. The microstructure of the obtained ZnO were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), the I-V characteristics were measured by using semiconductor characterization system. With the experimental results, effect of high pressure and temperature treatment on the microstructure and varistor properties of ZnO nanocrystals, were investigated.Firstly, the variety of morphology, grain sizes, and structure of the samples under different temperature and pressure were studied. The SEM and XRD results show: all of the samples in our experiment present a hexagonal wurtzite structure. The nanocrystals eventually transform to bulk materials while the grain sizes increase with increasing the temperature under a certain pressure. It indicates that high temperature can obviously promote the growth of the grain. Respectively the ZnO nanocrystals show various evolutions with increasing the pressure under a certain temperature. Under the room temperature, the grain size decreases with increasing the pressure, while under the high temperature, the grain size increases with increasing the pressure. The differences were caused by pressure's two different kinds of effects on crystals, which is that under room temperature, the pressure-induced grain fragmentation takes on a more significant role, while under the high temperature, the growth of the grain caused by high temperature and pressure does. Below the 850℃, 6GPa treatment, the phase transformation of ZnO was not observed. Therefore, the research on the phase transformation of ZnO should be done under higher pressure and temperature conditions.Then, effect of high pressure and temperature treatment on the varistor properties of ZnO nanocrystals, were investigated. Under room temperature and high pressure, ZnO shows a high-resistance and linear electrical property. Relatively, the crystals processed under high temperature and pressure develop a nonlinear electrical property. The experimental results show that high pressure and temperature treatment can produce large grain and effectively decrease the varistor voltage. It can be a new method for preparing low varistor voltage Zone ceramic varistors. Meanwhile, it is found that the nonlinear coefficient changed under the high pressure and temperature treatment.