【作者】 方华为；

【导师】 田旭；

【作者基本信息】 武汉理工大学 ， 凝聚态物理， 2007， 硕士

【摘要】 本论文中，在六面顶压机上对氧化锌纳米晶进行了高温高压处理，用扫描电子显微镜和X射线衍射仪对处理后的样品的微观结构进行了表征，用半导体特性测量系统测试了样品的伏安特性。由实验结果，分析了高温高压处理对于氧化锌纳米晶的微观结构和压敏特性的影响。首先，我们考察了不同的温度和压力参数下氧化锌纳米晶的微观形貌、晶粒大小、相结构的变化。SEM像和XRD测试结果显示，本实验高温高压条件下的样品均为标准六方相纤锌矿结构。在一定压力下，随着处理温度的升高，氧化锌晶粒尺寸持续增大，逐渐由纳米级粒子转化为常规体相材料。表明高温条件可以促进晶粒生长。在一定温度下，随着处理压力的增大，氧化锌晶粒演化呈现不同的规律：在室温下，晶粒尺寸随着处理压力的增大而减小；在高温下，晶粒尺寸随着处理压力的增大而增大。文中利用压力对材料晶粒大小产生不同影响的两种效应对此作出了解释：室温下，压力导致的压致晶粒碎化效应占主导地位，而高温下，高温高压共同引起的晶粒长大占主导地位。低于850℃，6GPa的高温高压条件下，没有观测到氧化锌的新相。这表明要研究氧化锌的高压相变，需要在更高的温度和压力条件下进行。这将为今后进一步研究氧化锌的高压相变问题时，对温度和压力参数的选取提供参考依据。接着，本文研究了冷高压和高温高压处理对氧化锌纳米晶的压敏特性的影响。冷高压下，氧化锌呈现出高阻值的线性电阻特性。而经高温高压条件处理后的样品在相同的外部测试电场范围内，明显地显示出非线性电学特性。实验结果表明，高温高压调制可以得到充分长大的晶粒，从而显著降低氧化锌的压敏电压。这对于目前主要考虑通过掺杂、制备氧化锌薄膜使压敏电阻低压化的研究现状，无疑是提供了新的途径和研究方法。同时，我们发现，不同的高温高压处理条件对样品的非线性系数也会产生一定的影响。本文利用压敏电阻的双肖特基势垒模型对此作出了初步的解释。更多还原

【Abstract】 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.更多还原