热电转换作为一种绿色环保的能量转换技术，已受到人们的广泛关注。如何提高热电材料的转换效率已成为目前该领域的研究热点。本项目将以热电材料的微观结构作为研究重点，利用正电子湮没实验方法系统研究以Mg2Si和Bi2Te3为代表的热电材料的缺陷特性，以及缺陷对材料热电性能的影响，探讨从微观角度调控热电性能的有效途径。研究内容包括：1）利用正电子湮没寿命测量鉴别材料中的寿命成分，判断缺陷的种类和浓度；2）利用新发展的符合多普勒展宽技术测量电子动量分布，通过研究空位周围的化学环境，判断缺陷的不同种类；3）利用第一性原理计算正电子在自由态和缺陷态的湮没特征，增加鉴别缺陷种类的准确性；4）研究不同类型的空位对晶格热导率的影响，空位与载流子的相互作用及对电导率的影响，以及材料热电优值的变化，并借助固体理论计算，了解空位对热电性能改善的微观机理。项目研究结果将为有效提高热电器件转换效率提供重要指导。

Thermoelectric conversion has attracted much attention because it can convert waste heat into usable energy, which increases enenrgy efficiency and decreases pollutants. How to increase the conversion efficiency of thermoelectric materials has become an ative research field in recent years. Our project will put the aim on the mictrostructure of thermoelectric materials, and use positron annihilation spectroscopy to study the defect properties of Mg2Si and Bi2Te3 and their effects on the thermoelectric properties. We will try to find effective way to improve the thermoelectric properties from the microstructural point of view. The main contents include: 1)Study the nature and concentration of defects by measuring the various positron lifetime components in materials using positron lifetime spectroscopy; 2)Using the newly developed Coincidence Doppler Broadening technique to measure the momentum distribution of electrons and discriminate the different defects by studying the chemical environments around defects; 3)Calculate the positron annihilation characteristics in various positron states including free and trapped states by using first-principle calculations. Using the theoretical results to further confirm the defect discrimination; 4)Study the effects of different vacancy defects on the lattice thermal conductivity, the interaction between vacancies and free carriers, and the effect of vacancies on the electric conductivity. Find the effect of defects on the final figure of merit ZT of materials. By using the theoretical calculation, find the underlying mechanism for the improvement of the thermoelectric properties by vacancy defects. The results of this project will provide important guidance for the improvement of energy conversion efficiency of thermoelectric devices.