Chromium Chalcogenide based Thermoelectrics

对于许多商业过程，如内燃机，由于余热造成的损失是不可避免的。安装在热电发电机中的热电材料可以通过将存在的温度梯度转换为电压来部分恢复否则损失的能量。然而，目前高效的热电材料包括稀有和危险的元素，如铅、锑、碲等。基于铬硫化物的热电项目研究了二元(CrxCrS2)和三元(MCrS2(M=Cu，Ag))铬硫化物作为迄今尚未探索的热电材料。除了组成元素相对容易获得外，铬硫化物是已知的可以高度掺杂的半导体。因此，在不改变一般结构的情况下，可以在较宽的组成范围内取代阴离子和阳离子。在本项目中，将深入研究取代对实际结构和热电性能的影响，特别是Seebeck系数以及电导率和热导率。通过改变载流子数量和带隙宽度可以改变电导率。另一方面，由于附加的自旋熵，塞贝克系数可以想见地增加。通过取代和拓扑定向反应，引入特定的缺陷结构(点缺陷、平面缺陷和纳米沉淀物)，可以降低导热系数。为了使这些新的热电材料的化学、微观和纳米结构的性质合理化，必须使用透射电子显微镜和X射线衍射方法来研究合成、组成、(微)结构和热电性能之间的关系。这两种方法的结合允许在所有相关的长度尺度上对复杂材料建立完整的定量模型。在热电特性方面，将开发一种新型的测量装置，能够快速、可靠地测定大量样品的热电材料的特性变量。特别有希望的材料将通过原位和非原位的透射电子显微镜和X射线衍射加热实验进行详细的研究，以研究循环加热时的结构变化；这些变化将与热电性能的变化相关联。最后，该研究项目还解决了相关的应用技术主题，如制备用于集成在硫系铬系热电发电机中的低欧姆触点。因此，对基础研究提出了有吸引力的问题，一旦得到回答，热电社区将有望获得重大好处，如热电材料的长期稳定性和特定的故障机制。

For many commercial processes like combustion engines losses due to waste heat are inevitable. Thermoelectric materials mounted in a thermoelectric generator can partially recover the otherwise lost energy by converting the existent temperature gradient to an electrical voltage. However, current efficient thermoelectric materials consist of rare and hazardous elements like Lead, Antimony, Tellurium, etc.The project Chrome chalcogenide based Thermoelectrics investigates binary (CrxCrS2) and ternary (MCrS2 (M = Cu, Ag)) chrome chalcogenides as up until now unexplored thermoelectric materials. Besides the relative ease of accessibility of consisting elements, chrome chalcogenides are known semiconductors which can be highly doped. Hence, substitution of anions and cations is possible for a broad compositional range without alterations to the general structure. The influence of substitution on real structure and thermoelectric properties, especially Seebeck coefficient as well as electrical and thermal conductivity will be thoroughly investigated during this project.The electrical conductivity can be modified by changing the number of charge carriers and the width of the band gap. On the other hand, the Seebeck coefficient conceivably increases due to additional spin entropy. A decrease of the thermal conductivity can be achieved by substitution and topotactic reactions, introducing specific defect structures (point defects, planar defects and nanoprecipitates). To rationalize the chemical, micro- and nanostructural properties of these new thermoelectric materials challenging and partially novel to-be-developed Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) methods have to be used in order to investigate correlations between synthesis, composition, (micro)structure and thermoelectric properties. The combination of both methods allows a complete and quantitative model for complex materials on all relevant length scales. For the thermoelectric characterization, a new type of measurement set-up will be developed which enables quick and reliable determination of the characteristic variables for thermoelectric materials of numerous samples. Particularly promising materials will be investigated in detail by in and ex situ TEM and XRD heating experiments to investigate structural changes upon cyclic heating; these will be correlated to alterations of thermoelectric properties.Ultimately, this research project also addresses relevant application-technological topics like the preparation of low ohmic contacts for integration in chrome chalcogenide based thermoelectric generators. Therefore, appealing questions arise for basic research, upon answering; a significant benefit for the thermoelectric community can be expected, like long term stability of thermoelectric materials and the specific failure mechanism.