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Critical mode and band-gap-controlled bipolar thermoelectric properties of SnSe

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  • I. Loa
  • S. R. Popuri
  • A. D. Fortes
  • J. W. G. Bos

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https://link.aps.org/doi/10.1103/PhysRevMaterials.2.085405
Original languageEnglish
Article number085405
Number of pages7
JournalPhysical Review Materials
Volume2
Issue number8
DOIs
Publication statusPublished - 13 Aug 2018

Abstract

The reliable calculation of electronic structures and understanding of electrical properties depends on an accurate model of the crystal structure. Here we have reinvestigated the crystal structure of the high-zT thermoelectric material tin selenide, SnSe, between 4 and 1000 K using high-resolution neutron powder diffraction. Symmetry analysis reveals the presence of four active structural distortion modes, one of which is found to be active over a relatively wide range of more than ±200 K around the symmetry-breaking Pnma−Cmcm transition at 800 K. Density functional theory calculations on the basis of the experimental structure parameters show that the unusual, steplike temperature dependencies of the electrical transport properties of SnSe are caused by the onset of intrinsic bipolar conductivity, amplified and shifted to lower temperatures by a rapid reduction of the band gap between 700 and 800 K. The calculated band gap is highly sensitive to small out-of-plane Sn displacements observed in the diffraction experiments. SnSe with a sufficiently controlled acceptor concentration is predicted to produce simultaneously a large positive and a large negative Seebeck effect along different crystal directions.

    Research areas

  • SnSe, tin selenide, thermoelectric, crystal structure, electronic structure, DFT calculations, neutron diffraction crystallography

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