超离子晶体中的非简谐与无序声子散射及其对热传导的影响机制

Approximately 50% of the energy consumed by human being is wasted in the form of heat, therefore, waste heat recovery is of great significance. Thermoelectric materials with low thermal conductivities provide a potential solution for waste heat recovery. Much research effort has been devoted to reducing thermal conductivity based on phonon scattering via nano-particles or defects, whereas the study of intrinsic phonon scattering mechanisms is still lagging behind. The applicant’s previous research indicates that superionic crystal AgCrSe2 has an intrinsically ultra-low thermal conductivity; however, the phonon scattering mechanisms are still to be unveiled. In this project, the applicant aims to study the lattice dynamics and thermal transport in superionic crystals CuCrSe2, AgCrSe2 and AgCrS2 from the electronic and atomistic levels using advanced first-principles methods and large-scale neutron research facilities, and to uncover the phonon-phonon and disorder-phonon scattering mechanisms. Based on deeper insight into the lattice dynamics, the applicant will apply external stress and electric fields to manipulate the phonon scattering and thermal transport properties. This project will provide new design guidelines for the developments of low thermal conductivity materials.

当前人类能源消耗总量的大约50%都以废热的形式排放，对废热的有效回收具有重要意义。这一需求恰为低热导率热电能源转换材料的发展提供了契机。大量研究致力于引入纳米相或晶格缺陷等散射声子以降低晶格热导率，然而对低热导晶体中本征声子散射机制的研究却相对滞后。项目申请人前期的研究工作表明超离子晶体AgCrSe2具有极低的本征热导率与独特的声子散射机制。然而，目前仍然缺乏对超离子晶体声子耦合机制的微观定量描述。本项目旨在结合新发展的第一性原理计算方法与非弹性中子散射，从电子与原子层次深入系统地研究超离子晶体CuCrSe2、AgCrSe2与AgCrS2的非简谐声子-声子散射与无序-声子散射机制。在此基础之上，申请人将通过外加应力场与电场进一步调控超离子晶体的热输运性质。该项目将为新型低热导材料的研发奠定基础并提供方向指引。

由于当前部分人类能源消耗以废热形式排放，因此对热能的回收具有重要意义。这一需求为低热导热电能源转换材料的发展提供了契机。在本项目的执行过程中，我们结合第一性原理计算与机器学习构建了超离子晶体的原子间相互作用势函数，从电子与原子层次深入地研究了声子散射与热输运机制。通过与非弹性中子散射实验对比，我们验证了理论计算结果。我们的研究表明在布里渊区中心附近的长横波声子在超离子态下仍然可以保持有效传播，该结果加深了对横波声子在超离子态中输运机理的认识。另外，我们通过Green-Kubo方法的分析发现，除了常规的热传导之外，扩散引发的对流机制也会极大的影响超离子态中的热输运性质。