Phonon anharmonicity and negative thermal expansion in SnSe

Dipanshu Bansal, Jiawang Hong, Chen W. Li, Andrew F. May, Wallace Porter, Michael Y. Hu, Douglas L. Abernathy, and Olivier Delaire
Phys. Rev. B 94, 054307 – Published 9 August 2016

Abstract

The anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy, in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. The origin of the anharmonic phonon thermodynamics is linked to the electronic structure.

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  • Received 11 May 2016

DOI:https://doi.org/10.1103/PhysRevB.94.054307

©2016 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Dipanshu Bansal1,*, Jiawang Hong1, Chen W. Li1, Andrew F. May1, Wallace Porter1, Michael Y. Hu2, Douglas L. Abernathy3, and Olivier Delaire1,4,†

  • 1Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  • 2Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
  • 3Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  • 4Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA

  • *bansald@ornl.gov
  • olivier.delaire@duke.edu

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Issue

Vol. 94, Iss. 5 — 1 August 2016

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