Nanostructured materials for thermoelectric applications

目前与清洁能源的产生和使用有关的背景有利于基于热电材料的技术的发展。从这些材料中，可以制造各种称为TE模块的设备，这些设备没有移动机械部件，因此具有可靠的性能。这些模块可以在基于珀尔帖效应的冷却器模式下运行，也可以在利用废热发电的热电发电机模式下运行。热电材料的性能是从其优值来评价的。为了获得高的优值，材料应同时具有高导电性和低导热性。一些半导体具有这种特殊的行为，从而具有更好的TE性能。在各种降低热导率的方法中，最有前途的方法之一是生产纳米结构材料。由于纳米晶体之间的界面较多，晶格组分对热阻的贡献较大。在过去的几年里，我们在École Polytechnique的研究小组已经开发出一种基于粉末冶金碲化铋合金生产半导体合金的方法。该方法是通过机械合金化和热挤压合成合金。合金粉末的初步表征表明，亚微米大小的颗粒为多晶，晶粒尺寸在5 ~ 20 nm之间。提出的研究项目的目标是沿着块状热电材料的生产过程描述纳米结构材料的演变。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，我们还将验证用大块纳米结构TE合金制造的模块生产实际设备和系统的可行性。系统的性能将由我们的一个工业合作伙伴在项目中建造的真实冰箱上进行评估。他们还试验了各种系统，在100°C的低温下利用废热发电

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