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

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 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.
PHILOSOPHICAL MAGAZINE

Suggestions

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 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 mode Gruneisen parameter in the vicinity of the lambda-transition point in NH4Cl
Karacali, H.; Yurtseven, Hasan Hamit (2006-11-01)
This study gives our relations between the specific heat C P and the Raman frequency shifts (1/v)(partial derivative v/partial derivative T)(p) for the lattice modes of v(5) (144 cm(-1)) and v(5) (174 cm(-1)), when the mode Gruneisen parameter gamma(p) depends on the temperature near. the lambda-transition in NH4Cl (T-lambda = 242.5 K, P = 0).
Temperature Dependence of the Raman Frequency, Damping Constant and the Activation Energy of a Soft-Optic Mode in Ferroelectric Barium Titanate
Kiraci, A.; Yurtseven, Hasan Hamit (2012-01-01)
The Raman frequency of a soft-optic mode associated with the order parameter is calculated as a function of temperature from the mean field theory for barium titanate (T-C = 222K). Using the Raman frequencies calculated, the damping constant is evaluated and it is compared with the observed one for this soft-optic mode.
Temperature dependence of the isothermal bulk modulus of TiB2
Ozkan, H. (Elsevier BV, 2011-04-01)
The temperature dependencies of the isothermal bulk modulus of TiB2 above room temperature were calculated by using the equation for the Anderson- Gruneisen parameter (delta(T)) and its solution by Garai and Laugier (J. Appl. Phys. 101, 023514 (2007)). The present calculations utilize the relevant experimental data for the pressure derivative of the isothermal bulk modulus, K' as delta(T) in addition to the volume thermal expansion coefficients (alpha(V)). The temperature derivatives of the isothermal bulk ...
Citation Formats
H. Karacali and H. H. Yurtseven, “Temperature dependence of the Raman bandwidths and intensities of a lattice mode near the tricritical and second order phase transitions in NH4Cl,” PHILOSOPHICAL MAGAZINE, pp. 189–203, 2006, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/42684.