Browsing by Author "Yurtseven, H."

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Analysis of the IR-Raman Modes and the Heat Capacity Near the alpha-Inc-beta Transitions in Quartz
(2021) Yurtseven, H.; Gunay, E.; Karacali, H.; Ates, S.
This study gives our analysis for the temperature dependence of the infrared frequency and the integrated intensity of the 695 cm(-1) mode near the alpha-beta transition at 847.5 K and the temperature dependence of the Raman scattering cross section of the 355 cm(-1) mode near the beta-INC (incommensurate) transition which occurs within a small temperature (similar to 1.3 K) interval in relation to the order parameter in quartz. Both analyses are performed according to a power-law formula for the order parameter Q with the critical index beta using the experimental data from the literature. We also analyze the temperature dependence of the heat capacity C p according to the renormalization-group expression including first-order corrections to scaling term close to the alpha-INC-beta transitions in quartz by using the literature data. From our analyses, values of the critical exponent beta for the frequency and the integrated intensity of the 695 cm(-1) infrared mode and for the Raman scattering cross section of the 355 cm(-1) mode as a measure of the order parameter, are extracted. From the analysis of C p , the values of the critical exponent alpha are also extracted. Additionally, by means of scaling relations the critical exponent gamma of the isothermal compressibility kappa T and the renormalized components ( beta R , alpha R and gamma R ) are predicted for the alpha-INC-beta transitions in quartz. Our analyses given here indicate that weakly first-order transition occurs from the alpha phase to the incommensurate (INC) phase, which changes to the nearly second-order transition to the beta phase with increasing temperature in quartz, as also observed experimentally.
Calculation of the damping constant and the relaxation time of the LA mode in the incommensurate phase of quartz
(2021) Ates, S.; Yurtseven, H.
The damping constant (linewidth) of the LA mode is calculated as a function of temperature for the incommensurate (INC) phase of quartz by using the models of the pseudospin-phonon (PS) coupled and the energy fluctuation (EF). For this calculation, the observed linewidth (Gamma(LA)) data are used at P = 0 and 80.5MPa from the literature. Close to the incommensurate phase between the alpha and beta phases of quartz, the observed Gamma(LA) and the frequency shifts (Delta v(LA) ) are also analyzed by the power-law formula for both pressures (P = 0 and 80.5MPa). By using the Gamma(LA) and Delta v(LA), the inverse relaxation time (tau(-1)(LA)) is predicted as a function of temperature (P = 0 and 80.5MPa) in the incommensurate phase of quartz and the values of the activation energy (E-a) are deduced. Our calculated Gamma(LA) from both models (PS and EF) explain adequately the observed behavior of the linewidth of the LA mode in the incommensurate phase of quartz. Also, our predicted tau(-1)(LA) can be compared with the measurements in the INC phase of this molecular crystal.
Calculation of the Phase Diagrams (T - X and T - P) and the Thermodynamic Quantities for the Solid - Liquid Equilibria in n-tridecane
(2023) Tari, O.; Yurtseven, H.
solid - liquid equilibria in n-tridecane is investigated by calculating phase diagrams and the thermodynamic quantities using the Landau phenomenological model. By expanding the free energy in terms of the order parameter of the solid phase, the phase line equations are fitted to the experimental data for the T - X and T - P phase diagrams from the literature. The temperature dependences of the thermodynamic quantities (order parameter psi, susceptibility chi(psi), free energy F, the heat capacity C, entropy S and the enthalpy H) are predicted for the n-tridecane from this model. Our results give that the slope dT/dP congruent to 2 K/MPa for n-C-13 to n-C-17. psi varies with T as psi similar to(T - T-m)(1/2) above T-m. It is linear for the chi(-1)(psi), S(T) and C(T), and quadratic for the F(T) and H(T) in n-tridecane. This indicates that the Landau model, describes the observed behaviour of the phase diagrams satisfactorily for the solid - liquid equilibria in n-tridecane. Predictions of the thermodynamic quantities can also be compared with the measurements and predictions of some other theoretical models. The pressure effect, in particular, on the solid - liquid equilibria in n-tridecane can also be investigated under the model studied here.
Calculation of The Tilt Angle and Susceptibility for The Alpha-Beta Transition in Quartz Using A Mean Field Model
(2017) Yurtseven, H.; Ipekoglu, U.; Ates, S.
Tilt angle (order parameter) and the susceptibility are calculated as a function of temperature for the alpha-beta transition in quartz using a Landau phenomenological model. The tilt angle as obtained from the model is fitted to the experimental data from the literature and the temperature dependence of the tilt angle susceptibility is predicted close to the alpha-beta transition in quartz. Our results show that the mean field model explains the observed behavior of the alpha-beta phase transition in quartz adequately and it can be applied to some related materials.
Landau mean-field model with the cubic term for the alpha-beta transition in quartz
(2020) Ates, S.; Yurtseven, H.
Thermodynamic quantities are calculated as a function of temperature by using Landau mean-field model for the alpha-beta transition in quartz. By expanding the Gibbs free energy in terms of the order parameter (Q) with the cubic term (Q(3)), the temperature dependence of the relevant thermodynamic quantities are predicted using the heat capacity (C-P), which is fitted to the experimental data from the literature for the alpha-beta transition in quartz. Our results indicate that the Landau mean-field model is adequate to describe the first-order alpha-beta transition in quartz.
Pressure Effect on Thermodynamic Quantities for the Solid-Liquid Phase Transition in n-tridecane, n-hexadecane and n-octadecane
(INTERNATIONAL JOURNAL OF THERMODYNAMICS, 2024-04-17) Tari, O.; Yurtseven, H.
The pressure effect is investigated regarding the solid - liquid equilibria (SLE) in n-alkanes. Using the Landau phenomenological model, the pressure dependences of the thermodynamic functions are predicted and the phase diagrams are constructed for the solid - liquid transitions in the binary mixtures of n-alkanes. The experimental data from the literature are used for the phase diagrams in the mixtures. Our fits for the phase diagrams are reasonably good. Regarding the cubic dependence of the concentration (T - X, P - X) and the linear dependence of the pressure (P - T) on the temperature, our results show that the n-tridecane is distinguished from the other mixtures due to its lowest freezing temperature (T-1 = 291.08 K) and correspondingly higher concentration (x(1) = 0.1982). It is found that the divergence behaviour of the heat capacity (C) with the critical exponent 1/2 from the extended mean field model is in particular more apparent at the room temperature (293.15 K) at various pressures for the solid - liquid transition. This is accompanied with the pressure dependences of the order parameter, susceptibility, entropy and enthalpy for those mixtures as studied here.
Resonant frequency shifts related to the elastic constants near the alpha-beta transition in quartz
(2019) Yurtseven, H.; Ates, S.
The resonant frequency shifts of vibrational modes are related to the elastic constants at various temperatures for the alpha-beta transition in quartz (T-c = 573.0 degrees C for alpha-quartz and 574.3 degrees C for beta-quartz). This correlation is constructed on the basis of the spectroscopic modifications of the Pippard relations near the alpha-beta transition in quartz by using the observed data from the literature. Our results indicate that the elastic properties can be described from the spectroscopic parameters (frequency shifts) as we have studied here for the alpha-beta transition in quartz. Using those relations, elastic constants can also be obtained from the frequency shifts near the phase transitions of various crystalline systems. (C) 2018 Elsevier B.V. All rights reserved.
Temperature Dependence Of The Frequency Shifts Related To The Thermodynamic Quantities Close To Phase Transitions In Nano2
(PHASE TRANSITIONS, 2024-10-02) Yurtseven, H.; Sefer, O. Akay
This study examines a linear relationship between the frequency shifts, (1/W)(partial derivative w/partial derivative T)p, and the variation of the dielectric constant, (1/epsilon)(partial derivative epsilon/partial derivative T)p, close to phase transitions in ferroelectric crystalline systems, in particular, ferroelectric NaNO2 as studied here. Both quantities (frequency and dielectric constant) are described by the power-law formulae below the Curie temperature T-c (ferroelectric phase), T-c < T < T-i (incommensurate phase) and T > T-i (paraelectric phase). The divergence behaviour of the mode Gruneisen parameter (gamma(p)) is obtained, whose temperature dependence can also be described by a power-law formula in NaNO2. It is also shown that the heat capacity C-p can be evaluated from the thermal expansion (alpha(p)) by means of the same critical exponent since they exhibit similar critical behaviour near T-c and T-i in this crystal.
Temperature dependence of the piezoelectric resonance frequency in relation to the anomalous strain near the incommensurate phase of quartz
(2021) Ates, S; Yurtseven, H.
The temperature dependence of the piezoelectric resonance frequency is analyzed by the power-law formula in the vicinity of the critical temperature of the incommensurate (INC) phase in quartz using the experimental data from the literature. By considering the piezoelectric resonance frequency as an order parameter of the INC phase, correlation between the piezoelectric resonance frequency and the strain is constructed, which both decrease linearly with increasing temperature toward T-c in quartz. Our results can explain dynamics of the ordering mechanism in the INC phase (within a very narrow temperature interval between the alpha and beta phases of quartz) and suggest a second order transition from INC to the beta phase in quartz.