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Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe
Unai Aseginolaza1,2,3, Raffaello Bianco4,5,6, Lorenzo Monacelli4
1Centro de Física de Materiales CFM, CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5, 20018 Donostia, Basque Country, Spain.
Physical Review Letters
|March 9, 2019
Summary
Tin selenide (SnSe) exhibits excellent thermoelectric properties due to significant nonperturbative anharmonic effects. These anharmonic effects, particularly in vibrational modes, are crucial for understanding SnSe
Area of Science:
- Condensed matter physics
- Materials science
- Solid-state physics
Background:
- The layered semiconductor tin selenide (SnSe) is recognized as a highly efficient intrinsic thermoelectric material since 2014.
- Understanding the fundamental properties governing its thermoelectric performance is critical for technological applications.
Purpose of the Study:
- To investigate the vibrational and thermal transport properties of SnSe.
- To elucidate the role of anharmonic effects in the phase transition and thermoelectric efficiency of SnSe.
Main Methods:
- First-principles calculations were employed to study the material's properties.
- Analysis of phonon behavior, including zone-border phonon collapse, was performed.
- Lattice thermal conductivity was calculated, incorporating anharmonic scattering.
Main Results:
- Huge nonperturbative anharmonic effects significantly influence the vibrational and thermal transport properties of SnSe.
- The transition from the Cmcm to the Pnma phase is a second-order phase transition driven by the vanishing frequency of a zone-border phonon.
- Calculated lattice thermal conductivity shows good agreement with experimental data only when nonperturbative anharmonic scattering is included.
- Anomalous spectral functions with shoulders and double-peak structures were observed in in-plane vibrational modes.
Conclusions:
- Nonperturbative anharmonicity plays a critical role in the exceptional thermoelectric efficiency of SnSe.
- The observed phase transition mechanism and anomalous vibrational properties are directly linked to strong anharmonic effects.
- These findings provide fundamental insights into optimizing thermoelectric materials based on SnSe.
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