高压下TiO2和CuInX2(X=S, Se)能带结构及态密度的第一性原理研究

The changes of electrical transport properties have closed connection with energy band structure under pressure. Used first-principle method, the energy band structure and density of states were studied under pressure. It provides new ideas to further exploit the electrical properties of materials. Because of the energy shortage and environmental pollution, TiO2 and CuInX2(X=S, Se) as good performance alternative fuels, are widely researched. The first-principle calculation, which is based on the Density Functional Theory, is playing important role in computational materials. The theoretical analysis provided by first-principle calculation can not only explain the experimental phenomena, but can also provide a theoretical guide for the experiment. For example, the band gap and density of states of TiO2 and CuInX2(X=S, Se) can be explained the abnormal change of resistivity in high pressure experimental process. Furthermore, the high pressure system shows some novel properties, which can not be exist in the atmosphere pressure. The study will afford important evidence for solar cell researches and applications.

高压下材料电输运性质的变化与能带结构的压力效应紧密相连，为此我们利用第一性原理计算了不同压力下材料的能带结构及态密度，为进一步从理论上解释材料的性质提供了新的思路。由于能源短缺是目前全世界面临的重要问题，因此本项目选用目前制作太阳能电池的热门材料TiO2 和CuInX2(X=S, Se)为研究对象有着深远的意义。第一性原理计算是基于密度泛函理论和赝势方法，利用Material Studio中的Castep软件包完成的。计算得到压力作用下TiO2 和CuInX2(X=S, Se)带隙和电子态密度等一系列参数，揭示带隙与电学性质之间的相互关系，从理论上解释高压下电阻不连续变化的根本原因，进一步深入探讨相变机理。而且高压下太阳能电池材料的新奇性质对弥补其在常压下的不足，拓宽太阳能电池应用领域提供理论依据。

本研究采用高压在位电学测量与第一性原理计算相结合的方法，找到了压力作用下材料的电阻率反常变化的根本原因，为深入研究压力作用下材料相变机理提供了依据。其结论如下：.（1）对于氧化钛，柯铁矿结构更小的带隙是导致TiO2电阻率减小的根本原因；金红石氧化钛相变后带隙类型发生了改变，高压下材料晶界空间电荷势垒的降低是引起电阻减小的原因。.（2）CuInS2和CuInSe2常压和高压下均为直接带隙半导体，费米面附近的能态主要来自p态和d态电子的贡献，s态电子的贡献较少..（3）PbSe和PbTe高压下发生金属化相变，相变发生后带隙闭合。.上述结果证实了我们的实验结果和理论计算能够作为深入解释高压相变的依据。