The use of Raman frequency shifts of non-soft modes to provide detailed predictions of the critical behaviour of specific heat up to within a fraction of a degree of a second order (or weakly first order) phase transition is illustrated. As an example, the lambda-transition of ammonium chloride under ambient pressure has been studied, and values of critical exponents of a- almost-equal-to 0.76 and a+ almost-equal-to 0.82 have been derived for C(p) from the Raman data. This approach is believed to be valid for a wide range of systems showing second-order or weakly first-order phase transitions and it is possible to use it for relatively inaccessible samples such as those within high pressure enclosures.


Spontaneous polarization close to phase transitions in NaNO2
Yurtseven, Hasan Hamit; Tari, O (2001-08-01)
We give here the calculation of the order parameter and the spontaneous polarization as functions of temperature using the mean field model close to the phase transitions in NaNO2. We have fitted our calculated order parameter to the observed one from the literature. From this fitting, we have then calculated the spontaneous polarization as a function of temperature close to the phase transitions in NaNO2. Our calculated spontaneous polarization is in good agreement with the observed spontaneous polarizatio...
Critical behaviour of the dielectric constant for the smectic AC* transition under the electric field in ferroelectric liquid crystals
Yurtseven, Hasan Hamit (2012-01-01)
The temperature dependencies of the dielectric constant and the tilt angle (order parameter) are calculated under the electric field for the smectic A-smectic C* (AC*) transition in 4-(3-methyl-2-chlorobutanoyloxy)-4'-heptyloxybiphenyl (A7). The dielectric constant is fitted to the experimental data by using our mean field model with the biquadratic coupling between the spontaneous polarisation P and the tilt angle theta. Our results show that the mean field model with the P-2 theta(2) coupling describes sa...
Critical behavior of the spontaneous polarization and the dielectric susceptibility close to the cubic-tetragonal transition in BaTiO3
Yurtseven, Hasan Hamit (2015-09-01)
Using Landau mean field model, the spontaneous polarization and the dielectric susceptibility are analyzed as functions of temperature and pressure close to the cubic-tetragonal (ferroelectric-paraelectric) transition in BaTiO3. From the analysis of the dielectric susceptibility and the spontaneous polarization, the critical exponents are deduced in the classical and quantum limits for BaTiO3. From the critical behavior of the dielectric susceptibility, the spontaneous polarization can be described for the ...
Temperature dependence of the polarization, dielectric constant, damping constant and the relaxation time close to the ferroelectric-paraelectric phase transition in LiNbO3
Kiraci, A.; Yurtseven, Hasan Hamit (2017-01-01)
We calculate the order parameter (spontaneous polarization) and the inverse dielectric susceptibility at various temperatures in the ferroelectric phase of LiNbO3 for its ferroelectric-paraelectric phase transition (T-C =1260 K) using the Landau phenomenological model. For this calculation, the Raman frequencies of the soft optic mode (TO1) are used as the order parameter and the fitting procedure is employed for both the order parameter and the inverse dielectric susceptibility by means of the observed dat...
Escape of photoelectrons and Compton-scattered photons from an HPGe detector
Can, Cüneyt (Wiley, 2003-07-01)
The response function of a planar HPGe detector due to escape of photoelectrons and Compton-scattered photons was studied for a point source with 59.5 keV energy. It was shown that both mechanisms, in addition to Ge x-ray escape, leading to partial deposition of energy, could be observed in the same experiment. A Monte Carlo program was used to investigate these components of the response function. The results indicate that although the escape of scattered photons and Ge x-rays are of the same magnitude, th...
Citation Formats
W. SHERMAN and H. H. Yurtseven, “CRITICAL-VALUES FOR SPECIFIC-HEAT FROM RAMAN DATA,” JOURNAL OF MOLECULAR STRUCTURE, pp. 61–71, 1991, Accessed: 00, 2020. [Online]. Available: