CuMTe2(M=Al、Ga、In)热电材料缺陷形成及其对热导率影响的正电子湮没谱学研究

Thermoelectric conversion is a green energy conversion technology that converts heat energy into electrical energy. Therefore, researching and improving the thermoelectric material performance will be of great significance for improving energy utilization effectively. We will first introduce the formation of defect in CuMTe2 (M=Al、Ga、In) thermoelectric materials, then investigate the positron annihilation properties of different types of defect structures by positron annihilation spectroscopy, as well as the effects of different types of defects on the thermal conductivity. The main contents include: (1) Study the formation of different types of defects and the stability of defective structures by first principles calculations, explore the formation of complex defects through the diffusion of atoms around of vacancy defects, and calculate the thermal conductivity of the different defective structures by the molecular dynamics simulation. (2) Study the positron annihilation characteristics of vacancy defect (nano-clusters embedding) structures by theoretical calculation and experimental measurement of positron annihilation, and explore the relationships between defect type and characteristic parameter of positron annihilation, identifying the type of defect in materials. (3) Research on the thermal conductivity of materials with different types of defects, and explore the relationships between defect types and the changes of lattice thermal conductivity. The results of this project will provide an important theoretical guidance for optimizing the thermoelectric performance of CuMTe2 (M=Al、Ga、In) systems.

热电转换是一种可将热能转换成电能的绿色能源转换技术，因而研究和提高热电材料性能在有效提高能源利用效率方面具有重要意义。本项目将以CuMTe2(M=Al、Ga、In)热电材料晶体结构的缺陷形成为切入，运用正电子湮没谱学探究不同类型缺陷结构的正电子湮没特性，探讨缺陷类型对晶格热导率的影响。具体研究内容如下:（1）利用第一性原理计算探究不同类型缺陷的形成及结构稳定性，揭示空位型缺陷周围原子迁移形成复合缺陷的物理机制，运用分子动力学模拟方法计算材料缺陷态结构晶格热导率。（2）利用正电子湮没理论计算与实验测量探究空位型缺陷（及纳米团簇嵌入）体系的正电子湮没特性，分析晶体缺陷结构特征与正电子湮没特性参数的对应关系，鉴别材料中缺陷类型。（3）测量不同缺陷类型样品的热导率，分析不同类型缺陷对晶格热导率的影响。本项目研究结果将为优化CuMTe2(M=Al、Ga、In)体系的热电性能提供重要的理论指导。

缺陷工程是调控热电材料晶格热导率的有效方法，因而探究材料内部缺陷的形成机制及其对缺陷类型有效鉴别是非常有意义的。本项目利用第一性原理计算方法系统探究了CuInTe2点缺陷及复合缺陷形成的物理机制及缺陷体系的正电子湮没特性，结果表明缺陷形成能依赖于元素化学势。在CuInTe2中较容易形成Cu空位、阳离子反位等点缺陷及2VCu+InCu复合缺陷，In空位缺陷可通过Cu原子迁移方式转变为VCu+CuIn。缺陷体系正电子湮没寿命结果表明正电子对空位型缺陷较为敏感。构建不同比例Ga掺杂CuInTe2晶体结构，利用理论计算得到了晶格参数、能带结构、正电子湮没寿命及多普勒展宽随掺杂比例的变化关系，实验测量结果表明缺陷存在能够对晶格热导率进行调控。本项目还系统探究了笼状热电材料CoSb3的缺陷形成及正电子湮没特性，通过不同类型缺陷形成能计算及原子迁移模拟，明确了其缺陷形成的物理机制。缺陷结构体系正电子湮没理论计算结果表明VCo对晶体微观结构影响不大，而SbCo反位缺陷则会造成较大晶格畸变。以上研究结果主要从原子尺度对材料缺陷的形成及其正电子湮没特征进行了系统研究，有助于实现热电材料缺陷的调控及缺陷类型的准确鉴别。