title: Anharmonicity in the High-Temperature Cmcm Phase of SnSe: Soft Modes and Three-Phonon Interactions.
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.
authors: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
authors: Jonathan M
authors: JM
authors: Skelton
authors: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
authors: Lee A
authors: LA
authors: Burton
authors: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
authors: Stephen C
authors: SC
authors: Parker
authors: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
authors: Aron
authors: A
authors: Walsh
authors: Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea.
authors: Chang-Eun
authors: CE
authors: Kim
authors: Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea.
authors: Aloysius
authors: A
authors: Soon
authors: University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
authors: John
authors: J
authors: Buckeridge
authors: University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
authors: Alexey A
authors: AA
authors: Sokol
authors: University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
authors: C Richard A
authors: CR
authors: Catlow
authors: Elements Strategy Initiative for Structural Materials, Kyoto University, Kyoto Prefecture 606-8501, Japan.
authors: Atsushi
authors: A
authors: Togo
authors: Elements Strategy Initiative for Structural Materials, Kyoto University, Kyoto Prefecture 606-8501, Japan.
authors: Isao
authors: I
authors: Tanaka