Inelastic Neutron Scattering Study of defective half-Heusler Material

Typical Half-Heusler compounds, identified as promising high temperature thermoelectric materials due to their unexpected semiconducting nature and good thermal properties. Several HH compounds are recently found to contain high concentrations of vacancies. These vacancies exhibit some specific distributions, such as short-range ordering in Nb0.8CoSb and possible Zig-zag distribution in Eu2ZnSb2. Intriguingly, these vacancy defective compounds exhibit much lower lattice thermal conductivity than their counterparts without vacancies. Here, we synthesized a series of ZrCoSb vacancy-defective compounds that can control the degree of vacancy order and thermal conductivity without changing their composition. These defective ZrCoSb samples can be considered as a hierarchical structure of order at different length scales, short-range order in some samples and long-range order in others. However, a comprehensive understanding is missing due to the lack of an experimental measurements and analysis of lattice dynamics in those compounds. In this proposal, we want to apply neutron scattering technique to study the dynamic spectra, hence to assess the significance of vacancies in the suppression of lattice thermal conductivity.

典型的半赫斯勒化合物（Half-Heusler compounds）因意外的半导体特性与优良的热性能，被认定为极具潜力的高温热电材料。近期研究发现，若干半赫斯勒化合物中存在高浓度空位，这些空位呈现出特定分布规律——例如Nb₀.₈CoSb中的短程有序分布，以及Eu₂ZnSb₂中可能存在的锯齿状分布。有趣的是，此类含空位缺陷的化合物，其晶格热导率显著低于无空位的对应物。本研究合成了一系列ZrCoSb空位缺陷化合物，可在不改变成分的前提下调控空位有序度与热导率。这些缺陷ZrCoSb样品具有不同长度尺度上有序的层级结构：部分样品呈现短程有序，另一些则为长程有序。然而，由于缺乏对这些化合物晶格动力学的实验测量与分析，目前尚未形成全面理解。在此，我们拟应用中子散射技术研究其动态光谱，从而评估空位在抑制晶格热导率中的作用。