Temperature dependence of the Raman frequencies and bandwidths close to phase transitions in ammonium halides

Date

2001-09-01

Author

Yurtseven, Hasan Hamit

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In this study, we give the temperature dependence of our observed frequencies and bandwidths for the Raman optical modes in the ammonium halides close to the phase transitions of the first order (NH4 Br), tricritical (NH4Cl) and second order (NH4Cl). Using the predictions of an [sing pseudospin-phonon coupled model, which considers interactions between two spin and two phonons, our observed Raman data have been interpreted qualitatively. Our results show that an Ising model considered here can explain the observed behaviour of the Raman phonons near the phase transitions of the first order, tricritical and second order in the ammonium halides. (C) 2001 Elsevier Science B.V. All rights reserved

Subject Keywords

Raman spectroscopy, Phase transitions, Ising model, Ammonium halides

URI

https://hdl.handle.net/11511/52136

Journal

JOURNAL OF MOLECULAR STRUCTURE

DOI

https://doi.org/10.1016/s0022-2860(01)00519-1

Collections

Department of Physics, Article

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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, Hasan Hamit (2006-01-11) 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 latt...
Temperature dependence of the Raman bandwidths for the lattice and internal modes in ammonium halides close to the lambda-phase transitions Yurtseven, Hasan Hamit (2008-07-01) We study here the temperature dependence of our Raman bandwidths for the upsilon(5) lattice modes of NH4Cl (T-lambda = 241 K) and NH4Br (T-lambda = 235 K) and for the upsilon(2) internal mode of NH4Cl close to the lambda-phase transitions.
Temperature and Pressure Effect on the Raman Frequencies Calculated from the Crystal Volume in the gamma-Phase of Solid Nitrogen Yurtseven, Hasan Hamit (Springer Science and Business Media LLC, 2015-09-01) The temperature and pressure dependences of the Raman frequencies of the lattice modes (E-g and B-1g modes) and of an internal mode (2331 cm(-1)) are predicted using the observed molar volume data from the literature in the gamma-phase of solid N-2. This calculation is carried out by means of the mode Gruneisen parameter of each Raman mode in the gamma-phase of solid nitrogen. Our results show that the predicted Raman frequencies of the E-g mode increase as the pressure increases. The Raman frequencies of t...
Temperature dependence of the damping constant and the order parameter close to the lambda phase transitions in ammonium halides Yurtseven, Hasan Hamit (Elsevier BV, 2006-10-01) 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 bandw...
Critical behaviour of the Raman frequency shifts in the vicinity of the lambda-phase transition in NH4Br Yurtseven, Hasan Hamit (2006-01-01) This study gives the temperature dependence of the Raman frequencies for the lattice mode of upsilon(7) (TA) and the internal mode of upsilon(2) close to the X-phase transition (T-lambda=234K, P=\) in NB4Br.

Citation Formats

H. H. Yurtseven, “Temperature dependence of the Raman frequencies and bandwidths close to phase transitions in ammonium halides,” JOURNAL OF MOLECULAR STRUCTURE, pp. 47–55, 2001, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/52136.