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arXiv · 1807.07726

Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe

Unai Aseginolaza·Raffaello Bianco·Lorenzo Monacelli·Lorenzo Paulatto·Matteo Calandra·Francesco Mauri·Aitor Bergara·Ion Errea
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Abstract

Since 2014 the layered semiconductor SnSe in the high-temperature Cmcm phase is known to be the most efficient thermoelectric material. Making use of first-principles calculations we show that its vibrational and thermal transport properties are determined by huge non-perturbative anharmonic effects. We show that the transition from the Cmcm phase to the low-symmetry Pnma is a second-order phase transition driven by the collapse of a zone border phonon, whose frequency vanishes at the transition temperature. Our calculations show that the spectral function of the in-plane vibrational modes are strongly anomalous with shoulders and double-peak structures. We calculate the lattice thermal conductivity obtaining good agreement with experiments only when non-perturbative anharmonic scattering is included. Our results suggest that the good thermoelectric efficiency of SnSe is strongly affected by the non-perturbative anharmonicity. We expect similar effects to occur in other thermoelectric materials.

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Unai Aseginolaza, Raffaello Bianco, Lorenzo Monacelli, Lorenzo Paulatto, Matteo Calandra, Francesco Mauri, Aitor Bergara, Ion Errea. 2018-07-20. Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe. https://doi.org/10.1103/physrevlett.122.075901

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