Raman scattering study and symmetry aspects of the phase transition in ferroelastic Sb5O7I

W. Prettl and K. H. Rieder
Phys. Rev. B 14, 2171 – Published 1 September 1976
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Abstract

The low-frequency Raman spectra of ferroelastic Sb5O7I crystals have been measured for temperatures ranging from 295 K to well above the phase transition at Tc=481 K. A strongly damped soft mode which is present only in the ferroelastic phase and quasielastic scattering from a central line, whose intensity peaks around Tc, are observed. A symmetry analysis shows that the instability of the hexagonal high-temperature phase may be explained by assuming a triply degenerate soft mode belonging to the star of the zone-boundary M point in the Brillouin zone. An expression for the free energy consistent with symmetry is constructed and the relation between the spontaneous elastic strain and the soft-mode amplitudes are determined. Applying this phenomenological theory it is shown that the intensities of several Raman lines, which decrease with rising temperature and vanish above Tc, are a measure of the temperature dependence of the order parameter. The experimental results indicate that the phase transition is weakly discontinuous.

  • Received 8 March 1976

DOI:https://doi.org/10.1103/PhysRevB.14.2171

©1976 American Physical Society

Authors & Affiliations

W. Prettl

  • Fachbereich Physik der Universität Regensburg, Regensburg, Germany

K. H. Rieder

  • IBM Zürich Research Laboratory, 8803 Rüschlikon, Switzerland
  • Max-Planck-Institut für Festkörperforschung, Stuttgart 80, Germany

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Issue

Vol. 14, Iss. 5 — 1 September 1976

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