定向生长SnTe/Te共晶界面声子散射的微观机理研究

Thermoelectric conversion technology is one of the important ways to alleviate the world's energy shortage and environmental problems. Developing some large interface structure thermoelectric materials with low lattice thermal conduction becomes the key to the problem solving. In this project, the in situ eutectic SnTe/Te composite thermoelectric material was taken as the research object using the eutectic boundary interface phonon scattering experiment. Combining the theoretical analysis with atomic interface, the phonon scattering behavior of the micron scale atomic interface was investigated. A phonon scattering model of coupled grain boundary surfaces was established. The dynamic scattering process of phonon was characterized at the eutectic grain boundary. Based on the boltzmann heat transport equation and the correlative experimental results, a dynamic model of the conjugate interface phonon scattering was constructed, analyzing the decrease process of the lattice thermal conductivity. The different wavelength phonon scattering mechanism at conjugate interface structure was revealed. Additionally, directional solidification technology was used to growth a series of different organizated interface structure eutectic crystals. The phonon scattering behavior under the changeable interface structures were studied. The interface lattice thermal conductivity reduction process was represented to reveal the phonon scattering mechanism of material structure. This study presents a new thought for the investigation of phonon-scattering mechanism at the directional growth eutectic interface of SnTe/Te alloy. The conssequences not only make a common and deeper understanding of the phonon scattering processes and mechanism at the eutectic interfaces. It also will provide a great help in guiding the synthesis of high-performance thermoelectric materials and displying a profound values of academic research.

热电转换技术是缓解世界能源短缺和环境危机的一条重要途径，研究具有低声子热导界面结构的热电材料成为解决该问题的关键之一。本项目以原位共晶SnTe/Te热电材料为研究对象，基于共晶界面声子散射引发晶格热导率降低的实验结果，结合原子界面结构分析，研究微尺度界面结构对声子的散射行为，构建共晶界面声子散射模型，表征声子界面散射过程；并以玻尔兹曼热传输方程及实验结果为依据，建立共晶界面声子散射的动力学计算模型，分析声子热导率的衰减过程，深层次揭示共晶界面对不同波长声子的散射机理；同时采用定向凝固方法合成组织变化的界面结构，研究复杂界面结构的声子散射，表征微米尺度界面声子热导率的降低过程，揭示复杂界面结构的声子散射机理。本研究提出一种采用SnTe/Te共晶材料研究界面声子散射的新思路，其研究结果不仅对微观界面声子散射机理有更深入认识，而且对合成高性能热电材料有着重要的指导价值和学术研究意义。

低的晶格热导率是提高热电材料能量转化效率的关键，共晶热电材料由于具有大量的相界面可以对声子造成有效散射，实现晶格热导率的有效调控。项目以SnTe-Te共晶合金为研究对象，开展了晶格热导率第一性原理计算、材料制备、组织表征以及热电性能优化等方面的研究工作。基于第一性原理的非简谐晶格动力学计算结果表明大的声子群速度以及弛豫时间是SnTe合金具备较高晶格热导率的内在原因。采取元素掺杂Sb可以有效降低声子群速度，同时基体中富余Sb又以纳米析出相形式析出而增强声子散射，最终使得晶格热导率降低到0.57Wm-1K-1并接近理论极限值。项目研究通过熔体旋甩结合放电等离子烧结(MS-SPS)以及定向凝固两种工艺进行SnTe-Te共晶耦合组织制备，发现共晶合金不但可以获得较低的晶格热导率，同时还可以兼具SnTe优异的电导率以及Te高的Seebeck系数，实现电输运性能的优化。MS-SPS工艺制备的Sn-90at.%Te合金最大ZT值达到0.42，该值为相同温度下组成相SnTe的1.8倍、Te的2.1倍。研究还发现定向凝固制备的共晶合金热电性能具有明显的各向异性，以Sn-90at.%Te合金为例，633K下平行相界面方向和垂直相界面方向试样晶格热导率和ZT值分别为1.34 Wm-1K-1和1.02 Wm-1K-1以及0.23和0.40。该项目的研究成果不仅完善了热电材料声子传输机理，同时也为热电性能优化提供了指导。