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Title: Revisiting pressure-induced phase transition in silicon clathrates using Ge substitution

Ba 8Si 39Ge 7 and Ba 8Si 29Ge 17 have been studied at high pressure using x-ray diffraction and x-ray absorption spectroscopy (XAS) at the Ge K edge. In Ba 8Si 39Ge 7, a transition is observed similar to the one in Ba 8Si 46, apparently isostructural. However, the XAS data analysis shows that the transformation is related to the off-centering of the Ba atoms. A theoretical model based on a Landau potential suggests that this transition is second order, with a symmetry-breaking mechanism related to the Ba displacement probably initiated by the vacancy creation or local distortion predicted theoretically. Lastly, this analysis gives a coherent picture of the phase transition mechanism. In the case of Ba 8Si 29Ge 17, such phase transition is not observed as the Ba atoms appear already off-center at ambient pressure.
Authors:
ORCiD logo [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [1] ;  [4] ;  [1] ;  [1]
  1. Univ. of Lyon (France); Univ. Claude Bernard Lyon, Villeurbanne (France). Inst. Lumiere Matiere
  2. Univ. of Lyon (France); Univ. Claude Bernard Lyon, Villeurbanne (France). Inst. Lumiere Matiere; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Institut Néel, CNRS and Université Joseph Fourier, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble Cedex 9, France
  4. European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble, France
Publication Date:
Report Number(s):
LA-UR-17-22102
Journal ID: ISSN 2469-9950
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 93; Journal Issue: 13; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Material Science; Clathrates, pressure, phase transition, silicon, germanium
OSTI Identifier:
1351200