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arXiv · 1602.03762

Anharmonicity in the high-temperature Cmcm phase of SnSe: soft modes and three-phonon interactions

Jonathan M. Skelton·Lee A. Burton·Stephen C. Parker·Aron Walsh·Chang-Eun Kim·Aloysius Soon·John Buckeridge·Alexey A. Sokol·C. Richard A. Catlow·Atsushi Togo·Isao Tanaka
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Abstract

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 renormalisation 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.

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Jonathan M. Skelton, Lee A. Burton, Stephen C. Parker, Aron Walsh, Chang-Eun Kim, Aloysius Soon, John Buckeridge, Alexey A. Sokol, C. Richard A. Catlow, Atsushi Togo, Isao Tanaka. 2016-07-30. Anharmonicity in the high-temperature Cmcm phase of SnSe: soft modes and three-phonon interactions. https://doi.org/10.1103/physrevlett.117.075502

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