Yazar "Yurtseven, H." seçeneğine göre listele

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    ANALYSIS OF HEAT CAPACITY AND GLASS TRANSITION IN AMORPHOUS ICE
    (World Scientific Publ Co Pte Ltd, 2010) Yurtseven, H.; Kurt, M.
    We analyze the heat capacity C(P) for low and high-density amorphous ice below the transition temperature (T(C) approximate to 140 K) using a power-law formula. The renormalized critical exponent alpha(R) is extracted from the observed C(P) data, which describes similar critical behavior for both low and high-density amorphous ice below T(C). Our analysis can also describe a glass transition in the low-density amorphous ice which is made from the high-density amorphous ice at 124 K, as observed experimentally.
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    ANALYSIS OF THE FREQUENCY SHIFT AND THE LINEWIDTH AS A FUNCTION OF TEMPERATURE IN SOLID NITROGEN
    (World Scientific Publ Co Pte Ltd, 2011) Kurt, M.; Yurtseven, H.
    The temperature dependence of the frequency shift and the linewidth is studied using the expressions derived from the anharmonic self-energy. The functional form of the frequency shift is fitted in this study to the experimental data for the R(1) fluorescence line of ruby sample as a function temperature at zero pressure, instead of using empirical nu-P and nu-T relations in the ruby fluorescence method as given in the literature, in particular, for the solid nitrogen. We also demonstrate in this study the temperature dependence of the E(g) librational frequency and its linewidth by fitting the functional forms of both frequency shift and the linewidth to the experimental data for the alpha phase of solid nitrogen.
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    Analysis of the peak position and linewidth as a function of temperature for the phase transitions in LiKSO4
    (World Scientific Publ Co Pte Ltd, 2016) Yurtseven, H.; Kurt, M.
    Analysis of the peak position and the linewidths of various infrared modes is performed at high (300-850 K) and low (1.5-300 K) temperatures using the experimental data from the literature for LiKSO4 which exhibits a sequence of phase transitions. The temperature dependences of the frequency and the linewidth which are derived from the anharmonic self-energy are fitted to the observed peak positions and the linewidths of the S-O stretching modes (internal nu(3) modes at 1135 cm(-1) and at 1180 cm(-1)), peak position of the S-O bending nu(4) (internal) modes, the peak position and the linewidth of the Li mode at 429 cm(-1) (external mode), and of the infrared band at 363 cm(-1) for LiKSO4. Our calculated peak positions and the linewidths, which are in good agreement with the observed data show that the anharmonic self-energy model describes adequately the observed behavior of the successive phase transitions in LiKSO4.
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    Calculation of the infrared frequency and the damping constant (full width at half maximum) for metal organic frameworks
    (Iop Publishing Ltd, 2019) Kurt, M.; Yurtseven, H.; Kurt, A.; Aksoy, S.
    The rho(NH2) infrared (IR) frequencies and the corresponding full width at half maximum (FWHM) values for (CH3)(2)(NH2FeMII)-M-III(HCOO)(6) (DMFeM, M = Ni, Zn, Cu, Fe, and Mg) are analyzed at various temperatures by using the experimental data from the literature. For the analysis of the IR frequencies of the rho(NH2) mode which is associated with the structural phase transitions in those metal structures, the temperature dependence of the mode frequency is assumed as an order parameter and the IR frequencies are calculated by using the molecular field theory. Also, the temperature dependence of the IR frequencies and of the damping constant as calculated from the models of pseudospin (dynamic disorder of dimethylammonium (DMA(+)) cations)-phonon coupling (PS) and of the energy fluctuation (EF), is fitted to the observed data for the wavenumber and FWHM of the rho(NH2) IR mode of the niccolites studied here. We find that the observed behavior of the IR frequencies and the FWHM of this mode can be described adequately by the models studied for the crystalline structures of interest. This method of calculating the frequencies (IR and Raman) and FWHM of modes which are responsible for the phase transitions can also be applied to some other metal organic frameworks.
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    Calculation of the Raman and IR frequencies as order parameters and the damping constant (FWHM) close to phase transitions in methylhydrazinium structures
    (Elsevier Science Bv, 2019) Kurt, M.; Yurtseven, H.; Kurt, A.
    Temperature dependences of the frequencies for the Raman modes of v (NH2), v(s) (CH3), v(1) (HCOO-), vs (CNN) and IR mode of rho (NH2) are calculated in particular, for MHyMn close to the phase transition temperature (T-C = 220 K) in the family of compounds CH3NH2NH2 M(HCOO)(3), MHyM with M = Mn, Mg, Fe and Zn. By assuming Raman and infrared frequency as an order parameter, this calculation is performed from the molecular field theory by using the experimental data from the literature. We also calculate the damping constant (FWHM) from the order parameter (Raman and IR frequency of those modes) by using the pseudospin (MHy(+) cations)-phonon coupled model (PS) and the energy-fluctuation model (EF) for methylhydrazinium metal formate frameworks. Expressions of the damping constant from both models are fitted to the observed FWHM data for the Raman and infrared modes studied for these metal formates. Our results show that the anomalous behaviour of the Raman and IR frequencies of those modes, except the v(S)(CH3) Raman mode which are associated with the phase transition can be described adequately by the molecular field theory in MHyM, as observed experimentally. Also, the damping constant calculated from the PS and EF models can explain the observed FWHM of those Raman and IR modes studied in methylhydrazinium metal formate frameworks. (C) 2019 Elsevier B.V. All rights reserved.
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    Calculation of the Specific Heat Close to Phase Transition in S-triazine
    (Walter De Gruyter Gmbh, 2009) Kurt, M.; Yurtseven, H.
    The specific heat C-V as a function of temperature has been calculated using the quasi-harmonic and mean field approximation for s-triazine close to the transition temperature (T-C=198 K). Using the parameters for the shear strain angle (order parameter) fitted to the observed Raman frequencies of the four bands, the specific heat C-V is calculated from the free energy of s-triazine. The calculated C-V values show no anomaly in comparison with the experimentally observed C-P which exhibits a sharp peak near T-C in s-triazine.
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    Calculation of the tilt angle and susceptibility as functions of temperature and the electric field close to the Sm A - Sm C* transition in C7
    (Canadian Science Publishing, Nrc Research Press, 2018) Aksoy, S.; Yurtseven, H.; Kurt, M.
    Smectic A - Smectic C* transition in the ferroelectric liquid crystal (C7) is studied as a function of the electric field and the temperature. By expanding the free energy in terms of the tilt angle theta (Smectic C* phase) and the polarization P with a linear coupling between theta and P (P theta) in mean field theory, the tilt angle is calculated as a function of the electric field (theta versus E) at constant temperatures with respect to the transition temperature for C7 using the observed data from the literature. Also, by extracting the tilt angle from the observed electric displacements at various temperatures (at constant field strength) the inverse tilt angle susceptibility (chi(-1)(theta)), derived from the free energy, is fitted to the observed data for the dielectric constant and the fitted parameters are determined. Our calculated theta and chi(theta). show that the mean field theory explains adequately the observed behavior of the Smectic A - Smectic C* transition in the liquid crystals C7.
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    PIPPARD RELATIONS MODIFIED FOR THE RAMAN FREQUENCY SHIFTS CLOSE TO I-II PHASE TRANSITION IN S-TRIAZINE
    (World Scientific Publ Co Pte Ltd, 2011) Yurtseven, H.; Kurt, M.
    The pressure dependence of the frequency shifts 1/omega(partial derivative omega/partial derivative T)(P) is calculated from the 1/omega(partial derivative omega/partial derivative P)(T) for the Raman modes I and IV according to the spectroscopic modifications of the Pippard relations. The observed Raman frequencies of those modes are used for this calculation close to the I-II phase transition in s-triazine. From the frequency shifts, the isothermal compressibility kappa(T) and the specific heat C-P are also calculated as a function of pressure close to the I-II phase transition in s-triazine. Our calculated values of 1/omega(partial derivative omega/partial derivative T)(P) kappa(T) and C-P can be compared with the experimental measurements at various pressures in the phases I and II of s-triazine.
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    Pressure dependence of the Raman frequency shifts related to the thermodynamic quantities in phase II of s-triazine
    (Indian Assoc Cultivation Science, 2011) Yurtseven, H.; Kurt, M.
    The temperature-induced frequency shifts (1/omega)(a,omega/a,T) (p) are calculated from the pressure induced frequency shifts (1/omega)(a,omega/a,P) (T) using the observed frequencies at various pressures for the Raman modes of II and III in phase II (P > P (C) ) of s-triazine. The values of the mode Gruneisen parameters gamma (T) (isobaric) and gamma (T) (isothermal) of those Raman modes studied here, are determined through the Pippard relations in the spectroscopically modified forms for this crystal. The temperature-induced and the pressure-induced frequency shifts are then used to predict the pressure dependence of the isothermal compressibility, thermal expansion and the specific heat in phase II (P > P (C) ) of s-triazine.
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    Sm A - ferroelectric-Sm C transition in the mixture of C7+10.O.4 and in the ferroelectric C7
    (Taylor & Francis Ltd, 2020) Aksoy, S.; Kurt, M.; Yurtseven, H.
    Tilt angle and the dielectric constant (susceptibility ) as functions of the field strength and temperature, respectively are calculated from the Landau phenomenological model and they are fitted to the observed data from the literature for the Sm A - Sm C* transition in the mixture of C7 + 10.O.4. Values of the critical exponents for the order parameters (tilt angle and polarization P) and tilt angle susceptibility of C7 and of the (dielectric constant) of the mixture C7 + 10.O.4 close to are extracted from the power-law formula. Our results indicate a second-order and a weakly first-order Sm A - Sm C* transitions for C7 + 10.O.4 and C7, respectively as also observed experimentally.
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    Temperature dependence of the order parameters (spontaneous polarisation and the tilt angle) at various concentrations for a mixture of SCE9+SCE10
    (Taylor & Francis Ltd, 2012) Yurtseven, H.; Kurt, M.
    The smectic A- smectic C* (AC*) transition in a binary mixture of SCE9+SCE10 is studied at various concentrations of SCE9 near (x(c) = 0.12) and above xc (tricritical concentration). The temperature dependences of the spontaneous polarisation and the tilt angle (order parameters) are calculated using our mean field model with the bilinear and biquadratic couplings between these two order parameters. The expressions derived from the mean field model are fitted to the experimental data from the literature and the coefficients given in the free energy are determined. It is demonstrated that our mean field model explains the observed mean field to tricritical behaviour in SCE9+SCE10.
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    Temperature Dependence of The Raman Frequency Shifts Related to The Specific Heat and Thermal Expansion Close To I-II Phase Transition in S-Triazine.
    (Walter De Gruyter Gmbh, 2010) Kurt, M.; Yurtseven, H.
    A linear variation of the specific heat C-p with the frequency shifts 1/omega(partial derivative omega/partial derivative T)(p) is established for the Raman modes I-V at various temperatures (P=0) close to I-II phase transition in s-triazine (T-c=198 K). As an extension of this work, the temperature dependence of the thermal expansion alpha(p) is predicted from the frequency shifts and by the gamma(p) values deduced for the Raman modes studied close to the I-II phase transition in s-triazine. Our predicted alpha(p) can be examined by the thermodynamics measurements of the thermal expansion at various temperatures at zero pressure in both phases I and II of s-triazine.
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    TILT ANGLE AND THE TEMPERATURE SHIFTS CALCULATED AS A FUNCTION OF CONCENTRATION FOR THE AC* PHASE TRANSITION IN A BINARY MIXTURE OF LIQUID CRYSTALS
    (World Scientific Publ Co Pte Ltd, 2011) Yurtseven, H.; Kurt, M.
    We study here the tilt angle and the temperature shifts as a function of concentration for the AC* phase transition in a binary mixture, using our mean field model with the biquadratic P-2 theta(2) coupling - and also with the bilinear P theta and P-2 theta(2) couplings. By expanding the free energy in terms of the tilt angle and polarization, the tilt angle and the temperature shift, are evaluated by using the coefficients given in the free energy expansion. By employing a concentration-dependent coefficient, the tilt angle and the temperature shift are calculated as a function of concentration of 10.O.4 for the SmAC* transition in a binary mixture of C7 and 10.O.4. Our calculated values of the tilt angle and the temperature shifts decrease as the concentration of 10.O.4 increases, as confirmed experimentally for the AC* transition in this binary mixture. This indicates that our mean field models studied here are satisfactory to explain the observed behavior of the AC* transition of the binary mixture of C7 and 10.O.4.