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 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.

Original languageEnglish
Article number075502
JournalPhysical review letters
Volume117
Issue number7
DOIs
Publication statusPublished - 2016 Aug 10

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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    Skelton, J. M., Burton, L. A., Parker, S. C., Walsh, A., Kim, C. E., Soon, A., Buckeridge, J., Sokol, A. A., Catlow, C. R. A., Togo, A., & Tanaka, I. (2016). Anharmonicity in the High-Temperature Cmcm Phase of SnSe: Soft Modes and Three-Phonon Interactions. Physical review letters, 117(7), [075502]. https://doi.org/10.1103/PhysRevLett.117.075502