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Elastic constants and softening of acoustic modes in A2MX6-crystals observed by Brillouin scattering

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Zeitschrift für Physik B Condensed Matter

Abstract

Room-temperature Brillouin-scattering measurements of the longitudinal and transverse sound velocities for the cubic crystals K2SnCl6, K2ReCl6, (NH4)2SnCl6 and (NH4)2SiF6 are presented. The elastic constantsc 11,c 12 andc 44 are determined from the angular variation of the Brillouin line shifts. Furthermore, for K2SnCl6 the sound velocities in the [100]- and [111]-direction are investigated as a function of temperature, 256K≦T≦330K. A strong softening of thec 11–c 12 mode is observed in the para-distortive phase as the temperature approaches the phase transition temperatureT c1=262K from above, whilec 44 shows no anomaly within the experimental error. These acoustic anomalies are interpreted theoretically by a mechanism based on the coupling of the elastic strain field to the fluctuations of the soft-mode coordinates.

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Authors and Affiliations

  1. Institut für Experimentalphysik VI, Ruhr-Universität Bochum, Postfach 102148, D-4630, Bochum, Germany

    W. Henkel & J. Pelzl

  2. Institut für Theoretische Physik III, Ruhr-Universität Bochum, Universitätsstraße 150, D-4630, Bochum, Germany

    K. H. Höck

  3. Institut für Physik, Universität Basel — Theoretische Physik —, Klingelbergstraße 82, CH-4056, Basel, Switzerland

    H. Thomas

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  1. W. Henkel
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  2. J. Pelzl
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  3. K. H. Höck
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  4. H. Thomas
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Work supported by the Deutsche Forschungsgemeinschaft and the Swiss National Science Foundation

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Henkel, W., Pelzl, J., Höck, K.H. et al. Elastic constants and softening of acoustic modes in A2MX6-crystals observed by Brillouin scattering. Z Physik B 37, 321–332 (1980). https://doi.org/10.1007/BF01352742

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  • DOI: https://doi.org/10.1007/BF01352742

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