Critical behaviour of the Raman frequency shifts in the vicinity of the lambda-phase transition in NH4Br

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.
HIGH TEMPERATURE MATERIALS AND PROCESSES

Suggestions

Calculation of the Raman frequency and the damping constant (linewidth) of the stretching modes for the metal-organic compound DMMg close to the paraelectric-ferroelectric transitions
Yurtseven, Hasan Hamit (2018-01-01)
We calculate the Raman frequencies of the two stretching modes of as a function of temperature close to the paraelectric-ferroelectric transition (Tc = 270K) in (CH3)(2)NH2Mg(HCOO)(3) referred as DMMg. By assuming that the Raman frequencies of those two modes which exhibit anomalous behaviour near Tc due to the ordering of the dimethlyammonium cations (DMA(+)) as observed experimentally, are associated with the spontaneous polarization (order parameter), their Raman frequencies and damping constants are pre...
Calculation of the Raman frequency as a function of pressure for the phases of I, III, IV and V in cyclohexane
Yurtseven, Hasan Hamit (2014-06-05)
The Raman frequencies of the v(5) mode are calculated as a function of pressure up to 10 GPa (room temperature) for the phases I, III, IV and V of cyclohexane using the volume data from the literature by means of the isothermal mode Griineisen parameter gamma(T) of this mode.
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...
Ultrasonic frequencies calculated for the q[100] mode in the first-order, tricritical and the second-order phase transitions of NH4Cl
Yurtseven, Hasan Hamit (2001-06-01)
This study correlates the volume changes to the ultrasonic frequencies of the q[100] mode of NH4Cl for the first-order, tricritical and the second-order phase transitions in this crystal. Using these correlations we were able to calculate the ultrasonic frequencies of this mode at the pressures of 0, 0.6 and 1.1 kbar (first-order), 1.6 kbar (tricritical) and 2.15 kbar (second-order) by means of the volume change data from the literature. Our calculated frequencies are in good agreement with the observed dat...
Spectroscopic modifications of the Pippard relations for NaNO2 in the sinusoidal antiferroelectric phase
Tari, O; Yurtseven, Hasan Hamit (2002-06-01)
We establish in this study a linear variation of the specific heat C-p with the frequency shifts (1/nu)(partial derivativenu/partial derivativeT) in the sinusoidal antiferroelectric phase of NaNO2, according to the first Pippard relation which we have modified spectroscopically. For this linear relationship we use the Brillouin frequencies of acoustic phonon modes for the q[010], q[001] and q[100] modes of NaNO2 in the sinusoidal antiferroelectric phase. We then calculate dT/dP values due to those modes stu...
Citation Formats
H. H. Yurtseven, “Critical behaviour of the Raman frequency shifts in the vicinity of the lambda-phase transition in NH4Br,” HIGH TEMPERATURE MATERIALS AND PROCESSES, pp. 143–147, 2006, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/54191.