(Cu,Ag)2Se材料的电子-声子输运特性与热电性能研究

三元(Cu,Ag)2Se材料具有高载流子迁移率和极低晶格热导率，有望成为新型高性能热电材料。然而，(Cu,Ag)2Se材料均存在复杂的相变，相变前的低温相存在多种晶体结构，而相变后的高温相具有快离子导体特性，这为该体系电、热输运性质的研究增加了困难。深刻理解不同相变特征、晶体结构以及离子导电行为对(Cu,Ag)2Se材料电、热输运的影响机制是该类材料热电性能优化的关键。本项目拟以(Cu,Ag)2Se材料为研究对象，通过对具有不同Cu/Ag比例的(Cu,Ag)2Se材料的低温相晶体结构的解析、相变区域电输运性质的精细表征、高温相离子导电行为的系统测试，并结合基于第一性原理的电子结构和声子谱计算，探讨(Cu,Ag)2Se体系中化学组成、晶体结构、离子导电及相变对电子、声子输运的影响机制，建立热电输运性能与相变和离子迁移行为之间的内在关联性，并基于此设计合成(Cu,Ag)2Se基高性能热电材料。

Recently, (Cu,Ag)2Se-based chalcogenides have attracted worldwide attention as one kind of potential high performance thermoelectric materials because of their high carrier mobility and extreme low lattice thermal conductivity. However, investigation on the electron/phonon transport mechanism in (Cu,Ag)2Se materials is very difficult since the inherent physical features in (Cu,Ag)2Se such as complex phase transition, various crystal structure in the low-temperature phase, and superionic behavior in the high-temperature phase. A clear understanding on the relationship between these physical features and electron/phonon transport is critical for the thermoelectric performance optimization in (Cu,Ag)2Se. Therefore, in the present project, we will systematical investigate the electrical and thermal transport mechanism of the low-temperature (Cu,Ag)2Se phase with different crystal structure. We will also study the relationship between superionic conductor behavior and thermoelectric properties in the high-temperature (Cu,Ag)2Se phase. In addition, the relationship between phase transition and thermoelectric properties will be also discussed through detailed characterization and analysis of the thermoelectric properties during the (Cu,Ag)2Se phase transition. Combined with the first principle calculation, the influence of crystal structure, phase transition and superionic conducting behavior on electron/phonon transport mechanism can be obtained. It is expected that this project can develop several new high performance thermoelectric materials, and provide a deep understanding on the mechanisms for the electron and phonon transports in (Cu,Ag)2Se.