Anharmonicity in the High-Temperature Cmcm Phase of SnSe: Soft Modes and Three-Phonon Interactions
Anharmonicity in the High-Temperature Cmcm Phase of SnSe: Soft Modes and Three-Phonon Interactions
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DOI：
10.1103/physrevlett.117.075502
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发表时间：
2016-08-10
影响因子：
8.6
通讯作者：
Tanaka, Isao
中科院分区：
文献类型：
--
作者：
Skelton, Jonathan M.;Burton, Lee A.;Tanaka, Isao
层状半导体SnSe是已知性能最高的热电材料之一。我们证明，通过第一性原理晶格动力学研究，高温CMCM相是一个动态平均在较低的对称性极小值分离非常小的能量障碍。与低温Pnma相相比，Cmcm相显示出声子软化和增强的三声子散射，导致低频模式的非谐阻尼，从而导致热输运。我们开发了一个重正化方案来量化软模式对计算的性能的影响，并确认非谐性是Cmcm相位的固有特征。这些结果表明，热绝缘体和热电材料的设计概念，基于位移不稳定性，并突出了材料表征的晶格动力学计算的力量。
The layered semiconductor SnSe is one of the highest-performing thermoelectric materials known. We demonstrate, through a first-principles lattice-dynamics study, that the high-temperature Cmcm phase is a dynamic average over lower-symmetry minima separated by very small energetic barriers. Compared to the low-temperature Pnma phase, the Cmcm phase displays a phonon softening and enhanced three-phonon scattering, leading to an anharmonic damping of the low-frequency modes and hence the thermal transport. We develop a renormalization scheme to quantify the effect of the soft modes on the calculated properties, and confirm that the anharmonicity is an inherent feature of the Cmcm phase. These results suggest a design concept for thermal insulators and thermoelectric materials, based on displacive instabilities, and highlight the power of lattice-dynamics calculations for materials characterization.