(Cu,Ag)2Se材料的电子-声子输运特性与热电性能研究

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.

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。

快离子导体热电材料具有适中的电输运性质和极低的晶格热导率，成为了近几年热电研究领域的热点方向。本项目以(Cu,Ag)2Se材料为研究切入点，探讨了快离子导体热电材料体系中化学组成、晶体结构、离子导电及相变对电子、声子输运的影响机制，并基于此设计合成了一系列新型高性能热电材料。主要研究结果如下：.1. 我们首先研究了三元(Cu,Ag)2Se材料中不同Cu/Ag比例与物相组成、晶体结构、热电性能之间的关联，发现当CuAgSe满足化学计量比1:1:1时，材料具有最高的热电性能，其ZT值在440 K约为0.6，该结果发表于J. Mater. Chem. A, 2015, 3, 13662。在Se位引入Te固溶，我们给出了优化CuAgSe热电性能的方向，即通过提高材料的载流子浓度以减少少子对电输运性质的贡献，可以进一步提高ZT，该结果发表于J. Mater. Chem. A, 2015, 3, 22454。.2.我们开发了利用脉冲激光沉积技术制备CuAgSe薄膜的工艺，通过对衬底、气氛、气压、沉积时间等参数的调控，成功在玻璃衬底上和氩气气氛（2 Pa）下获得了具有优良热电性能的高质量CuAgSe薄膜。同时，我们还探讨了Ag2Se薄膜的生长工艺和Cu缺位对CuxS二元化合物晶体结构、相转变、以及热电性能的影响机制。相关结果分别发表于Ceramics International, 42, 2016, 12490-12495和APL Materials, 4, 2016, 104805。.3.我们基于Yokota提出的理论，发展了可以进行混合导体中离子电导率测量的“离子阻挡法 ”，并自主搭建了相应测试设备，探讨了电流大小、样品尺寸等各种因素对测试准确性的影响。利用该设备，测量了几种Cu基快离子导体热电材料的离子电导率，并计算了其离子激活能 (J Inorg. Mater., 32, 2017, 1337-1344)。.本项目的研究加深了对于快离子导体热电材料的研究，获得了2种新型的高性能热电材料，并对相关材料中的离子迁移行为进行了初步解析。目前受本项目资助论文共5篇，专利2项，顺利完成了研究目标。