Temperature dependence of the damping constant and the order parameter close to the lambda phase transitions in ammonium halides

Yurtseven H., Karacali H.

SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, vol.65, no.2, pp.421-427, 2006 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 65 Issue: 2
  • Publication Date: 2006
  • Doi Number: 10.1016/j.saa.2005.10.054
  • Journal Name: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.421-427
  • Keywords: damping constant, Raman bandwidths, ammonium halides, T-lambda, RAMAN-SCATTERING, OPTICAL PHONONS, T-LAMBDA, FREQUENCY, CRYSTALS, VIBRATIONS, DISORDER, SULFATE, SPECTRA
  • Middle East Technical University Affiliated: Yes

Abstract

This study gives our calculation for the damping constant, using the expressions derived for an Ising pseudospin-phonon coupled system in the ammonium halides (NH4Cl and NH4Br). For this calculation of the damping constant, we use the temperature dependence of the order parameter calculated from the molecular field theory. We predict here the damping constants for the v(5) (174 cm(-1)) and v(5) (177 cm(-1)) Raman modes of NH4Cl and NH4Br, respectively, below T-lambda and compare them with our observed bandwidths measured as a function of temperature for those phonon modes at zero pressure.