介观分级结构热电材料结构与性能机理研究

Thermoelectrics arise as one of the hot topics in energy materials because of their promising applications in solid refrigeration and waste heat conversion. The performance of conventional thermoelectric materials was supressed due to bottleneck factors. It has been demonstrated that the thermoelectric properties can be improved significantly by artificially construct hierarchical structures extending from nano-, meso- to micro scales, which can tune the transport of charge, phonon carriers effectively. Nevertheless, the physical mechanism underpinning the influence of thermoelectricity imposed by hierarchical structures remains an unresolved but key issue, owing to the inherent limitations of various structural tools. The conventional tools cannot be relied to uncover the tranport mechanism at different scales. In this project, we mainly investigate the novel thermoelectrics with high thermoelectricity (e.g. chalcogenides, oxides, intermetallics). We attempt to address several fundamental issues on nano, meso and microscales, such as inter and intra domain phonon and charge transport, mesoscale thermoelectricity, through a synergy among infrared spectroscopy, X-ray absorption spectroscopy and X-ray diffraction available at the synchrotron facilities at Shanghai, Beijing, and Hefei , as well as Density Functional Theory and Molecular Dynamics. The main goal is to illustrate the relationship between hierarchical structures and thermoelectricity, offering experimental evidences and theoretical guides for designing new thermoelectrics. The multi-scale structural tool based on synchrotron can be extrapolated to investigate the hierarchical structures in other similar functional materials, bearing important academic significances.

热电材料因固体制冷、废热转化等重要用途成为能源材料研究的热点之一。传统热电材料的性能遭遇瓶颈因素制约。研究表明，通过构筑纳米、介观到微米尺度分级结构，可调控电荷、声子载流子的输运，能显著提高材料的热电性能。然而，由于结构探测手段局限性，分级结构影响热电性能的物理机制仍属悬而未决的关键问题，常规的结构分析无法揭示不同尺度的输运机制。本项目拟以具有介观分级结构的新型高性能热电材料(如硫基化物、氧化物、金属互化物）为着眼点, 依托于上海光源等国内三大同步辐射装置，利用红外谱学及X射线谱学与衍射手段，结合密度泛函理论工具、分子动力学理论工具，从纳米到介观、微观尺度上，研究畴内畴间电子、声子传输、介观热电机制等关键科学问题, 旨在阐明分级结构-性能之间的关系，为新热电材料设计提供实验依据和理论指导。基于同步辐射的多尺度分级结构探测手段将能够拓展到同类功能材料的分级结构研究中，具有重要的学术价值。

热电材料的层级结构调控近年来成为热电性能调控的重要手段之一。这种方法主要通过建立从纳米尺度到介观、微米尺度分级结构，实现对电荷、声子载流子输运通道的有效调控，优化材料热电性能，进而提高其能源转化效率。本项目旨在从原子尺度上对晶格结构及其动力学的表征出发，发展基于同步辐射谱学技术的多层级结构探测技术手段，深入阐释这种分级结构有效调控热电性能的机制。本项目深入研究了多种新型热电材料的多晶、单晶体系的局域结构、声子模等动力学特征的谱学表征，基于上海光源等大科学装置，挖掘X射线谱学手段在局域结构、原子对振动信息的独特优势；结合国外装置中的远红外太赫兹反射谱学技术手段，对光学声子模进行了深入研究。初步阐明分级结构影响热电性能的构效关系，为新型热电材料设计提供基础实验数据提供设计原则指导。基于对大装置联合实验方法的前期探索，对相关技术手段实现所存在的挑战有了更加深刻的认识，对未来光源束线相关技术的发展提供设计思路。