Nanostructured materials for thermoelectric applications

目前与生产和使用清洁能源有关的情况有利于开发基于热电材料的技术。从这些材料中，可以制造各种称为TE模块的设备，这些设备没有移动的机械部件，从而获得可靠的性能。这些模块可以根据帕尔蒂埃效应在较冷的模式下运行，也可以在热电发电机模式下运行，在热电发电机模式下，电力由余热产生。热电材料的性能是从它们的优值系数来评价的。要获得较高的优值系数，材料应同时具有较高的电导率和较低的导热系数。一些半导体具有这种特殊的行为，提供了更好的TE性能。在各种降低导热系数的方法中，最有希望的方法之一是制备纳米结构材料。由于纳米晶体之间有更多的界面，晶格成分对热阻的贡献更大。在过去的几年里，我们在爱科尔理工学院的研究小组开发了一种从粉末冶金中生产基于碲化铋合金的半导体合金的方法。该方法包括机械合金化合成合金，然后热挤压。合金粉末的初步表征表明，亚微米级的颗粒是多晶的，颗粒尺寸在5-20 nm之间。拟议的研究项目的目标是表征纳米结构材料在块状热电材料生产过程中的演变。纳米结构的研究和分析将借助先进的X射线衍射和透射电子显微镜技术进行。在项目过程中，我们还将验证生产实际设备和系统的可行性，这些设备和系统使用块状纳米结构TE合金制造的模块。系统的性能将在我们在该项目中的一个工业合作伙伴制造的真实冰箱上进行评估。他们还试验了在100摄氏度左右的低温下利用废热发电的各种系统

The present context related to the generation and use of cleaner energy favors the development of technologies based on thermoelectric (TE) materials. From those materials, it is possible to fabricate various devices called TE modules that have no moving mechanical parts resulting in reliable performances. The modules can be operated in cooler mode based on Peltier effect or in thermoelectric generator mode where electricity is produced from waste heat. The performance of thermoelectric materials is evaluated from their figure of merit. To obtain high values of the figure of merit, the material should have at the same time high electrical conductivity and low thermal conductivity. Some semiconductors have this particular behavior giving better TE properties. Among the various approaches for reducing thermal conductivity, one of the most promising is to produce nanostructured materials. By having more interfaces between nanocrystals, higher contribution of thermal resistance comes from the lattice component. During the last years, our research group at École Polytechnique has developed a method to produce semiconductor alloys based on bismuth telluride alloys from powder metallurgy. The method consists in alloy synthesis by mechanical alloying followed by hot extrusion. Preliminary characterization of the alloyed powders revealed that particles of sub-micron size are polycrystalline with grain size in the range 5-20 nm. The goal of the proposed research project is to characterize the evolution of nanostructured materials along the production process of bulk thermoelectric materials. The study and analysis of the nanostructures will be done with the help of advanced X ray diffraction and transmission electron microscopy techniques. Within the course of the project, we will also verify the feasibility to produce actual devices and systems built with modules fabricated by using bulk nanostructured TE alloys. The performance of systems will be evaluated on real refrigerators build by one of our industrial partner in the project. They also experiment various system for electricity generation from waste heat at low temperatures on the order of 100°C