Temperature dependence of the Raman bandwidths and intensities of a lattice mode near the tricritical and second order phase transitions in NH4Cl

Karacali H., Yurtseven H.

PHILOSOPHICAL MAGAZINE, vol.86, no.2, pp.189-203, 2006 (SCI-Expanded) identifier

  • Publication Type: Article / Article
  • Volume: 86 Issue: 2
  • Publication Date: 2006
  • Doi Number: 10.1080/1478630500375167
  • Journal Name: PHILOSOPHICAL MAGAZINE
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.189-203
  • Middle East Technical University Affiliated: Yes

Abstract

We calculate here the temperature dependence of the damping constant using the expressions derived from the Matsushita's theory and the temperature dependence of the order parameter from the molecular field theory for the tricritical (1.5 kbar) and second order (2.8 kbar) phase transitions in NH4Cl. Our calculations are performed for the nu(5) (174 cm(-1)) Raman mode of NH4Cl for the pressures studied. Predictions for the damping constant are in good agreement with our observed Raman bandwidths of this lattice mode for both pressures. The Raman intensities calculated from the molecular field theory by means of the order parameter are also in good agreement with our observed Raman intensities of the nu(5) (174 cm(-1)) mode for both tricritical (1.5 kbar) and second order (2.8 kbar) phase transitions in NH4Cl. In this study our observed Raman intensities of this lattice mode are analysed using a power-law formula with the critical exponent beta for the order parameter at those two pressures considered in NH4Cl. From our analysis, the value of beta=0.5 is obtained as the mean. eld value.