Thermoelectric materials in the alloy system Bi2Te3-In2Te3

块体纳米结构热电材料是目前最有前途的高效热电器件材料。在本项目中，我们的目标是控制微结构的形成相对于几个微观结构的功能，从介观到纳米级的大块热电材料Bi 2 Te 3-In 2 Te 3和评估的热电性能的微观结构-性能关系。计划工作的新奇在于对微观结构形成的上级控制，因为化学均匀性、晶体取向和晶界密度将独立设计，从而实现最佳热电性能。到目前为止，文献中记录的这种材料的结果主要涉及的微观结构表征的各向同性多晶样品，辅以少量的热电性能的测量，但没有系统的组合测量的数据。本项目的第一步是制备具有均匀In浓度和降低的晶界密度的Bi 2 Te 3基取向晶体。发展了一种带籽晶的定制区熔技术，以控制化学成分和晶体取向，旨在生成化学均匀的Bi 2 Te 3单晶。为了选择合适的样品和种子浓度，实验评估了Bi_2 Te_3-In_2 Te_3系统的伪二元相图。在第二步中，将首次对定向晶体进行热处理实验，以在Bi 2 Te 3基质中产生纳米结构沉淀物，其中将通过透射电子显微镜（TEM）以高空间分辨率进行详细表征，包括关于纳米结构颗粒周围的取向关系、组成和应力状态的统计。最后，将对制备的纳米结构材料进行热电测量，旨在建立纳米结构与热电性能之间的关系。结合化学均匀性，晶体生长的优选取向和微观结构的长度尺度的控制将允许利用这些功能的影响塞贝克系数，热电性能各向异性和热导率，分别。因此，预期Bi 2 Te 3-In 2 Te 3的热电“品质因数”的显著增强。

Bulk nanostructured thermoelectric materials are at present considered as the most promising components for high efficiency thermoelectric devices. In the present project, we aim to control microstructure formation with respect to several microstructural features from the meso- to the nanoscale in the bulk thermoelectric material Bi2Te3-In2Te3 and evaluate the microstructure-property relationships with respect to the thermoelectric properties. The novelty of the planned work is in the by far superior control of microstructure formation, as chemical homogeneity, crystal orientation and grain boundary density will be designed independently such that optimum thermoelectric properties are achieved. Results so far documented in the literature on this material mainly concern the micro-structural characterization of exclusively of isotropic polycrystalline samples, complemented by a small number of measurements of thermoelectric properties, but no data of systematic combined measurements. The first step of the present project is to prepare Bi2Te3 based oriented crystals with homogeneous In concentration and reduced grain boundary density. A tailored zone melting technique with seed crystal is developed to control both chemical composition and crystal orientation, aiming to generate chemically homogeneous Bi2Te3 single crystals. For choosing an adequate concentration of sample and seed, the pseudo-binary phase diagram of the Bi2Te3-In2Te3 system is assessed experimentally. In a second step, for the first time heat treatment experiments will be performed on the oriented crystals for generating nanostructured precipitates in the Bi2Te3 matrix, of which detailed characterization including statistics on orientation relationship, composition and stress state around nanostructured particles will be performed via Transmission Electron Microscope (TEM) at high spatial resolution. Finally, thermoelectric measurements will be carried out on the prepared nanostructured materials, aiming to build the relations between the nanostructure and thermoelectric performance. Combining the control of chemical homogeneity, crystal growth preferred orientation and microstructural length scales will allow to exploit the impact of these features on Seebeck coefficient, thermoelectric property anisotropy and thermal conductivity, respectively. Consequently a significant enhancement of the thermoelectric "figure of merit" of Bi2Te3-In2Te3 is expected.