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.


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 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...
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...
Measurement of differential cross sections for the production of a pair of isolated photons in pp collisions at root s=7TeV
Chatrchyan, S.; et. al. (Springer Science and Business Media LLC, 2014-11-01)
A measurement of differential cross sections for the production of a pair of isolated photons in proton-proton collisions at root s = 7 TeV is presented. The data sample corresponds to an integrated luminosity of 5.0 fb(-1) collected with the CMS detector. A data-driven isolation template method is used to extract the prompt diphoton yield. The measured cross section for two isolated photons, with transverse energy above 40 and 25 GeV respectively, in the pseudorapidity range vertical bar eta vertical bar ...
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...
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: