Low Frequency Raman Spectra of Ionic Crystals

  • R. S. Krishnan
  • N. Krishnamurthy
  • T. M. Haridasan
  • J. Govindarajan

Abstract

Several physical phenomena depend on the normal modes of vibration of the crystal. A ferroelectric phase transition in an ionic crystal is explained as due to a vanishing low frequency transverse optical mode at q → 0 (soft mode)[1]. An antiferroelectric transition is due to a vanishing zone boundary phonon[2]. Phase transformations induced by pressure are similarly explained as due to a vanishing transverse acoustic phonon[3]. Order-disorder transformations in alloys are due to coupling of modes which are close in energy and at a phase difference π/2 [4]. These low frequency phonons can be easily observed in Raman spectra, though the far infra-red measurements are very difficult. The ferroelectric soft mode and its frequency variation have been observed by Perry et al[5] in Raman scattering.

Keywords

Calcite Nitrite Lanthanum Ferro Aragonite 

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Copyright information

© Springer Science+Business Media New York 1969

Authors and Affiliations

  • R. S. Krishnan
    • 1
  • N. Krishnamurthy
    • 1
  • T. M. Haridasan
    • 1
  • J. Govindarajan
    • 1
  1. 1.Department of PhysicsIndian Institute of ScienceBangaloreIndia

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