新型二维热电材料的高通量筛选与计算

发布时间：2018-03-18 16:30

本文选题：第一性原理　切入点：二维材料　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：热电材料是一种能将电能和热能相互转换的功能性材料,且具有全固态、体积小、可靠性高、无噪声无污染等优点。在环境污染和能源问题日益严重的今天,热电材料在汽车尾气废热发电、热电-光伏复合太阳能电池等方面的潜在应用得到了世界范围内研究者们的广泛关注。而如何获得高性能的热电材料是推进其广泛应用的至关重要的一环,也是当前研究的热点问题。上世纪九十年代,Hicks和Dresselhaus提出量子限域效应可以有效的增强超晶格体系的热电性能,为寻找热电性能较好的低维体系提供了理论支持。随着本世纪初石墨烯的成功制备,自支撑二维材料作为低维体系中的新成员,获得了广泛的关注。二维材料中的电子被限制在平面内运动,由于量子限域等效应,有可能比体相材料有着更优异的热电性质,引发了理论和实验工作者的极大研究热情。同时,材料建模和模拟技术的成熟以及“材料基因组”框架下高通量计算理念的发展,为寻找新型二维热电材料提供了有力的工具。本文将通过高通量筛选无机晶体结构数据库的方法,得到可能的二维材料的晶格结构;然后基于第一性原理的高通量计算,得到并分析二维材料的能带结构以及应力对能带结构的调控作用;最终基于玻尔兹曼输运方程的计算,虚拟筛选出具有高热电性能的二维材料。本文首先在无机晶体结构数据库(Inorganic Crystal Structure Database,ICSD)中筛选出89种可能剥离成为二维材料的层状体材料,获得其对应二维材料的晶格结构,并将89种二维材料按空间群分类。然后计算并对比了体相及二维相的磁性与能带结构。从计算结果中得知,有22种体相材料具有磁性,在剥离成二维材料后,其中9种材料磁矩大小不变,8种材料的磁矩减小,5种材料的磁矩增大。能带结构的计算表明,在由体相剥离为二维材料后,10种材料发生了间接到直接带隙转变,6种材料发生了直接到间接带隙转变。有13种二维材料在面内双轴应力的作用下发生了带隙类型的改变,其中8种是在拉伸应力下,5种在压缩应力下。最后计算了带隙大于零的二维材料的功率因子随载流子浓度的变化关系,发现p型的单层Bi2Te3材料具有最高的功率因子,并且功率因子的值较其体材料提升了约3倍。本文的计算结果表明,当层状体相材料剥离成二维材料后,维度的降低会改变其中一些材料的磁矩和能带结构,进而提升二维材料的热电性能。面内双轴应力也可以对材料的能带结构进行有效调控。本文的结果对加深二维材料物理特性的认识,设计新型二维热电材料,以及拓展二维材料在半导体纳米器件方面的应用具有积极的意义。
[Abstract]:Thermoelectric material is a kind of functional material which can convert electric energy and heat energy. It has the advantages of solid state, small volume, high reliability, no noise and no pollution, etc. Nowadays, environmental pollution and energy problems are becoming more and more serious. Thermoelectric materials are used to generate electricity in the waste heat of automobile exhaust, Potential applications such as thermoelectric-photovoltaic composite solar cells have attracted worldwide attention. How to obtain high-performance thermoelectric materials is a crucial part of its wide application. In -10s, Hicks and Dresselhaus proposed that the quantum limiting effect can effectively enhance the thermoelectric properties of superlattices. With the successful preparation of graphene at the beginning of this century, the self-supporting two-dimensional material is regarded as a new member of the low-dimensional system. The electrons in two-dimensional materials are confined to the in-plane motion. Due to the effects of quantum limiting field, it is possible that the two-dimensional materials have better thermoelectric properties than bulk materials. This has aroused great enthusiasm among theoretical and experimental workers. At the same time, the maturation of material modeling and simulation techniques and the development of high-throughput computing concepts within the framework of "material genomes", This paper provides a powerful tool for finding new two-dimensional thermoelectric materials. In this paper, the lattice structure of the possible two-dimensional materials is obtained by high-throughput screening of inorganic crystal structure databases, and then the high-throughput calculations based on first-principles are carried out. The energy band structure of two-dimensional material and the effect of stress on energy band structure are obtained and analyzed. Finally, the calculation of Boltzmann transport equation is carried out. In this paper, 89 kinds of layered materials which may be stripped into two-dimensional materials are selected from the inorganic crystal structure database, Inorganic Crystal Structure Database, and the lattice structure of the corresponding two-dimensional materials is obtained. The magnetic and band structures of the bulk phase and the two-dimensional phase were calculated and compared. From the results of the calculation, 22 kinds of bulk materials were found to have magnetic properties, which were separated into two dimensional materials. The magnetic moment of 9 kinds of materials is invariant and the magnetic moment of 8 kinds of materials is reduced. The calculation of energy band structure shows that the magnetic moment of 5 kinds of materials increases. The direct to indirect band gap transition occurred in 10 kinds of materials, and the band gap types of 13 two dimensional materials changed under the action of in-plane biaxial stress, and the direct to indirect band gap transition occurred in 6 kinds of materials. Eight of them are under tensile stress and five are under compression stress. Finally, the variation of power factor with carrier concentration in two-dimensional materials with band gap greater than zero is calculated. It is found that p-type monolayer Bi2Te3 materials have the highest power factor. And the power factor is about three times higher than that of the bulk material. The calculated results show that the reduction of the dimension will change the magnetic moment and the band structure of some of the materials when the layered materials are stripped into two-dimensional materials. The in-plane biaxial stress can also effectively regulate the energy band structure of the two-dimensional material. The results in this paper can deepen the understanding of the physical properties of the two-dimensional material and design a new two-dimensional thermoelectric material. And expand the application of two-dimensional materials in semiconductor nanodevices has positive significance.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB34

【相似文献】