Calculation of the specific heat for ND4Br close to phase transitions

This study gives our calculation for the specific heat close to the phase transitions from the disordered (phase 11) to the antiferro-ordered (phase 111) and to the ferro-ordered (phase IV) phases in ND4Br. We calculate the specific heat C-VI due to the nearest-neighbour interactions between ND4+. tetrahedra in the ND4Br crystal, by using an Ising model superimposed on an Einstein and/or Debye model which we have developed. Our calculated specific heat C-VI agrees well with the experimental C-p data for the phases 11, 111 and IV in ND4Br. This shows that our model is adequate to describe the observed behaviour of the ND4Br crystalline system close to its upper (T-c = 214.86 K) and lower (T-c = 166.7 K) transitions.


Calculation of the Brillouin frequencies close to phase transitions in NaNO2
Yurtseven, Hasan Hamit (2002-01-01)
We calculate here the Brillouin frequencies of the L-mode [010], [001] and [100] of NaNO2 for the phase transitions from the paraelectric phase to the sinusoidal anti-ferroelectric phase near the Neel temperature (T-N = 437.7 K) and to the ferroelectric phase near the critical temperature (T-c = 436.3 K) in this crystalline system. For calculating the frequencies, we use the thermal expansivity data for the phase regions considered, under the assumption that the mode Gruneisen parameter determined for each ...
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 P-T phase diagram of nitrogen using a mean field model
Enginer, Y.; Algul, G.; Yurtseven, Hasan Hamit (2017-12-20)
The P-T phase diagram is calculated at low and moderate pressures by obtaining the phase line equations for the transitions considered in nitrogen using the Landau phenomenological model. For some transitions, a quadratic coupling between the order parameters is taken into account in the expansion of free energies in terms of the order parameters. A quadratic function in T and P is fitted to the experimental P-T data from the literature and the fitted parameters are determined.
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.
Analysis of the frequency shifts close to the second order phase transition in NH4Cl
Yurtseven, Hasan Hamit (2001-03-01)
In this study we analyzed observed Raman data for the frequencies of the disorder-induced modes of v(7) (93 cm(-1)) and vs (144 cm(-1)) in the second order phase region of NH4Cl (P = 2.8 kbar). By means of a power-law formula describing the critical behaviour of the frequency shifts 1/v(partial derivativev/partial derivativeT)p for those phonon modes studied, we extract the critical exponent value of a = 0.25, which can also describe the critical behaviour of the specific hear Cp close to the second order p...
Citation Formats
H. H. Yurtseven, “Calculation of the specific heat for ND4Br close to phase transitions,” JOURNAL OF MOLECULAR STRUCTURE, pp. 29–34, 2002, Accessed: 00, 2020. [Online]. Available: