Tang Jianqin, Skelton Jonathan M
Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom.
J Phys Condens Matter. 2021 Mar 10;33(16). doi: 10.1088/1361-648X/abd8b8.
We present a systematic first-principles modelling study of the structural dynamics and thermal transport in CoSbskutterudites with a series of noble-gas filler atoms. Filling with chemically-inert atoms provides an idealised model for isolating the effects of the fillers from the impact of redox changes to the host electronic structure. A range of analysis techniques are proposed to estimate the filler rattling frequencies, to quantify the separate impacts of the fillers on the phonon group velocities and lifetimes, and to show how changes to the phonon spectra and interaction strengths lead to suppressed lifetimes. The noble-gas fillers are found to reduce the thermal conductivity of the CoSbframework by up to 15% primarily by suppressing the group velocities of low-lying optic modes. The filler rattling frequencies are determined by a detailed balance of increasing atomic mass and stronger interactions with the framework, and are found to be a good predictor of the impact on the heat transport. Lowering the rattling frequency below ∼1.5 THz by selecting heavy fillers that interact weakly with the framework is predicted to lead to a much larger suppression of the thermal transport, by inducing avoided crossings in the acoustic-mode dispersion and facilitating enhanced scattering and a consequent large reduction in phonon lifetimes. Approximate rattling frequencies determined from the harmonic force constants may therefore provide a useful metric for selecting filler atoms to optimise the thermal transport in skutterudites and other cage compounds such as clathrates.
我们对含有一系列稀有气体填充原子的钴锑方钴矿的结构动力学和热输运进行了系统的第一性原理建模研究。用化学惰性原子填充为将填充原子的影响与宿主电子结构氧化还原变化的影响隔离开来提供了一个理想化模型。我们提出了一系列分析技术来估计填充原子的晃动频率，量化填充原子对声子群速度和寿命的单独影响，并展示声子谱和相互作用强度的变化如何导致寿命的抑制。发现稀有气体填充原子主要通过抑制低频光学模式的群速度，使CoSb框架的热导率降低高达15%。填充原子的晃动频率由原子质量增加和与框架更强相互作用的详细平衡决定，并且被发现是对热输运影响的良好预测指标。通过选择与框架弱相互作用的重填充原子将晃动频率降低到约1.5太赫兹以下，预计会通过在声学模式色散中诱导避免交叉并促进增强的散射以及随之而来的声子寿命大幅降低，从而对热输运产生更大的抑制。因此，由简谐力常数确定的近似晃动频率可为选择填充原子以优化方钴矿和其他笼状化合物（如包合物）中的热输运提供有用的指标。
