多尺度声子输运调控优化Mg2Si基材料的热电性能

Mg2Si-based materials are environmentally friendly thermoelectric candidates applied at intermediate temperature, however, the reported conversion efficiency so far still cannot meet the requirement for commercial applications. Hierarchically organized microstructures with multi-scale defects can significantly reduce the lattice thermal conductivity, thus it is regarded as an effective emerging strategy to develop next generation of thermoelectric materials. This proposal aims to investigate the important physical quantities such as phonon lifetime, mean free path, and lattice thermal conductivity of Mg2Si-based materials by using the anharmonic lattice dynamics method based on first-principles calculations. With this method, we can further understand the impacts of point defect, embedded nanoinclusion, and grain boundary on phonon transport, so as to clearly illustrate the connections between microstructure and thermal conductivity, and to explore the physical mechanism of cooperatively manipulating phonon transports by panoscopic approach. Moreover, we will carry out synthesis, characterization and performance measurement for this series of materials. By combining the theoretic and experimental results, this research will lead to effective approaches to improve thermoelectric properties with thermal conductivity significantly reduced and electronic transport less affected, and provide theoretical insights for effective design and development of novel high performance Mg2Si-based thermoelectric materials.

Mg2Si基材料是一类环境友好的中温热电材料，然而其转换效率尚不能满足应用的要求。通过引入多尺度缺陷，分层次的微观结构设计能够显著降低晶格热导率，被视为开发下一代高性能热电材料的重要途径。本项目拟通过基于第一性原理计算的非简谐晶格动力学方法，求解Mg2Si基材料中的声子寿命、平均自由程和晶格热导率等重要物理量，在此基础上探索局部点缺陷、纳米镶嵌结构和纳米化晶界等多尺度缺陷对声子输运的影响规律，建立从材料微观结构到晶格热导率的直观物理图像，揭示全方位多尺度协同调控声子输运的物理机制。我们还将开展这一类热电材料的制备、表征和性能测试，结合理论研究和实验测量结果，提出保持优良电学性能、显著降低晶格热导率、提高材料热电性能的具体方案，为设计和优化新型高效Mg2Si基热电材料提供理论指导。

高性能热电材料需要尽可能高的功率因子和尽可能低的热导率，研究声子输运特性有助于理解材料晶格热导率的变化规律、为实验上进一步降低热导率提供指导、以及设计具有本征低热导率的新型热电材料。本项目采用第一性原理的非简谐晶格动力学方法，求解了Mg2Si1-xSnx固溶体和α-MgAgSb等热电材料中的声子寿命、平均自由程和晶格热导率等重要物理量，指出了Mg2Si1-xSnx固溶体中热导率的降低来源于声学声子频支的软化，α-MgAgSb的本征低热导率来源于其强非谐性。进一步的研究表明局域点缺陷对Mg2Si1-xSnx固溶体的热导率影响不大，而10 nm尺度的第二相结构可以继续材料的热导率。此外，我们将这种方法拓展到二维石墨炔材料中。相对于二维石墨烯材料，石墨炔中sp2-sp杂化的碳键结构不仅降低了声学频支和群速度，而且增加了散射几率显著削减了声子平均自由程，使得石墨炔表现出较低的热导率，有望应用为新型碳基高效热电材料。