Abstract

Understanding elementary excitations and their couplings in condensed matter systems is critical for developing better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The current record material for thermoelectric conversion efficiency, SnSe, has an ultralow thermal conductivity, but the mechanism behind the strong phonon scattering remains largely unknown. From inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and found the origin of the ionic-potential anharmonicity responsible for the unique properties of SnSe. We show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. The present results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers new insights on how electron–phonon and phonon–phonon interactions may lead to the realization of ultralow thermal conductivity.

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Acknowledgements

Neutron scattering measurements and analysis (O.D., C.W.L.) was supported as part of the S3TEC EFRC, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0001299. Computer simulations and analysis were supported through CAMM (J.H., D.B.), funded by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. Sample synthesis (A.F.M.) was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The use of Oak Ridge National Laboratory’s Spallation Neutron Source and High Flux Isotope Reactor was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. The orientation of single crystals was characterized using the X-ray Laue camera system at the X-ray lab in SNS, ORNL (we thank J. K. Keum for his assistance). This research used resources of the Oak Ridge Leadership Computing Facility (OLCF), which is supported by the Office of Science of the US Department of Energy.

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Author notes

    • C. W. Li
    •  & J. Hong

    These authors contributed equally to this work.

Affiliations

  1. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    • C. W. Li
    • , J. Hong
    • , A. F. May
    • , D. Bansal
    •  & O. Delaire
  2. Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    • S. Chi
    • , T. Hong
    •  & G. Ehlers

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Contributions

C.W.L. and O.D. performed the neutron scattering measurements with help from S.C., T.H. and G.E. J.H. and D.B. performed the first-principles simulations and lattice dynamics modelling. A.F.M. synthesized the samples. O.D., C.W.L. and J.H. wrote the manuscript and all authors commented on it. O.D. supervised the project.

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The authors declare no competing financial interests.

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Correspondence to C. W. Li or J. Hong or O. Delaire.

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https://doi.org/10.1038/nphys3492

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