Skelton, JM; Burton, LA; Parker, SC; Walsh, A; Kim, C-E; Soon, A; Buckeridge, J; ... Tanaka, I; + view all Skelton, JM; Burton, LA; Parker, SC; Walsh, A; Kim, C-E; Soon, A; Buckeridge, J; Sokol, AA; Catlow, CRA; Togo, A; Tanaka, I; - view fewer (2016) Anharmonicity in the High-Temperature Cmcm Phase of SnSe: Soft Modes and Three-Phonon Interactions. Physical Review Letters , 117 (7) , Article 075502. 10.1103/PhysRevLett.117.075502.

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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.

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