几种half-Heusler合金-SnSe异质结设计及其热电输运性质的理论研究

At present, the highest figure of merit reported experimentally is not more than 3.0. Therefore, it is particularly important to first theoretically design thermoelectric materials with excellent thermoelectric performance. In recent years, half-Heusler alloys and SnSe as star materials have been widely concerned by the thermoelectric community. Half-Heusler alloys are known for their high stability and high power factor, high thermal conductivity is not conducive to high ZT value，while SnSe is known for its low thermal conductivity. In this project, we will build half-Heusler alloys-SnSe heterojunctions, which are expected to achieve organic integration for the two kinds of materials, complementing each other with advantages, and thus to greatly improve the thermoelectric properties. The subject will uphold "structure determines performance, performance determines use" concept, and focus on the following three aspects using first principles calculations:.1. The most stable geometric structures of half-Heusler alloys-SnSe heterojunctions are determined. The electronic structure and phonon structure of half-Heusler alloys-SnSe heterojunctions are studied, and new phenomena and new characteristic are excavated..2. The thermoelectric properties of half-Heusler alloys-SnSe heterojunctions are investigated, and the effects of strain and electric fields on the thermoelectric properties of heterojunctions are discussed..3. Using electronic structure and phonon structure as the theoretical bridge, the inner connection between the geometric structures and the thermoelectric properties is revealed, and the physical origin is explored.

目前，实验上发现的热电材料其热电优值ZT最高的也不超过3。因此，从理论上先设计出热电性能卓越的热电材料显得尤为重要。近年来，half-Heusler合金和SnSe是被广泛关注的明星热电材料。half-Heusler合金以高稳定性、高功率因子见长，却因高热导率而不利于高ZT值，而SnSe则以低热导率见长。本课题将构建half-Heusler合金-SnSe异质结，有望实现两种材料的有机融合、优势互补来提高热电性能。本课题秉持“结构决定性能，性能决定用途”的理念，主要利用第一性原理探究物理本质，关注以下内容：.1.确定half-Heusler合金-SnSe异质结最稳几何结构。研究其电子结构和声子结构，并挖掘其中的新现象和新特性。.2.研究异质结热电性能，并讨论应变和电场对异质结热电性能的影响。.3.利用电子结构和声子结构这座理论桥梁揭示异质结几何结构和热电性能之间的内在联系，探究其中物理本源。

目前，热电材料的ZT值有待进一步提高，这样其才有可能被广泛应用。因此，有必要从理论上先设计出热电性能卓越的材料结构。项目原计划研究half-Heusler合金-SnSe异质结的热电输运性能，但考虑到此类异质结大都没有带隙给理论计算模拟研究带来不便。因此，在项目实际执行时，我们构建了四元X2YZM4型化合物-SnSe异质结，对其热电性能进行研究。也因此本项目相比于既定研究内容增加了以下研究内容：.1.研究了四元X2YZM4型化合物的几何结构、电子结构、热电性能。.2.研究了形变和电场对单层SnSe几何结构、电子结构的影响。.本项目提出好的热电材料的电子结构和声子结构应具备的特征，本项目不仅可供实验工作者参考，还能激发更多的理论研究。