Temperature dependence of the Raman bandwidths for the lattice and internal modes in ammonium halides close to the lambda-phase transitions

Date

2008-07-01

Author

Yurtseven, Hasan Hamit

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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.

Subject Keywords

Raman bandwidths, Ammonium halides, Lambda transition, ORDER-DISORDER TRANSITION, WEAKLY FIRST-ORDER, SINGLE-CRYSTALS, HEAT-CAPACITY, T-LAMBDA, NH4BR, NH4CL, PRESSURE, BROMIDE, FREQUENCY

URI

https://hdl.handle.net/11511/33363

Journal

SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY

DOI

https://doi.org/10.1016/.j.saa.2007.11.030

Collections

Department of Physics, Article

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Temperature dependence of the Raman frequencies and bandwidths close to phase transitions in ammonium halides Yurtseven, Hasan Hamit (2001-09-01) 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 o...
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 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...
Temperature Dependence of the Brillouin Frequency Shift and the Linewidth of the LA Mode in the Ferroelectric Phase of PZT-x (PbZr1-xTixO3) Yurtseven, Hasan Hamit; KİRACI, ALİ (2015-05-27) The temperature dependence of the Brillouin frequency and the linewidth of the LA mode is studied for the concentration of x=0.45 in the ferroelectric phase of PbZr1-xTixO3 (PZT-x) within the temperature range of 443 to 656 K (T-C=657 K). Using the experimental data for the Brillouin frequency of the LA mode as an order parameter below T-C the temperature dependence of the linewidth (FWHM) is calculated by the pseudospin-phonon coupled model and the energy fluctuation model for the lead titanate zirconate (...
Specific Heat of NH4Cl and NH4BrxCl1-x Crystals Close to the Ferro-Ordered Phase Yurtseven, Hasan Hamit (2009-04-01) This study gives calculation of the specific heat C-VI of NH4Cl and NH4BrxCl1-x under the Ising model for the transition between the disordered (D) and ferro-ordered O(F) phases in these crystalline systems. Our C-VI values which we calculated for x = 0 and x = 0.04, agree both below and above T-c with the observed C-p data from the literature. Our value of a congruent to 0.1 (T < T-c and T > T-c) is in good agreement with the predicted value of 1/8 (0.125) of a 3D Ising model.

Citation Formats

H. H. Yurtseven, “Temperature dependence of the Raman bandwidths for the lattice and internal modes in ammonium halides close to the lambda-phase transitions,” SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, pp. 445–448, 2008, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/33363.