Browsing by Author "Kiraci, Ali"

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Citation - WoS: 2
Citation - Scopus: 3
Analysis of the Integrated Intensity of the Central Peaks Calculated as a Function of Temperature in the Ferroelectric Phase of Lithium Tantalate
(Vinca inst Nuclear Sci, 2018) Yurtseven, Hamit; Kiraci, Ali; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The integrated intensity of the central peak is calculated as a function of temperature in the ferroelectric phase (T < T-C) of nearly stoichiometric LiTaO3. This calculation is performed using the temperature dependence of the order parameter obtained from the mean field theory at temperatures lower than the transition temperature T-C (T-C = 963 K) of this crystal. The calculated values of the order parameter (squared) are fitted to the integrated intensity of the central peaks as observed from the Raman and Brillouin scattering experiments as reported in the literature in the ferroelectric phase of nearly stoichiometric LiTaO3. Our results are in good agreement with the observed behavior of LiTaO3 crystal. Because of the applications of LiTaO3 in several academic disciplines including the material science and thermal science, it is beneficial to investigate dynamic properties of this crystal such as the damping constant, inverse relaxation time and the activation energy as also we studied here.
Citation - WoS: 1
Citation - Scopus: 1
Calculation of the Frequency Shifts and Damping Constant for the Raman Modes (A1g, B1) Near the Tetragonal-Cubic Transition in Srtio3
(Tubitak Scientific & Technological Research Council Turkey, 2017) Yurtseven, Hasan Hamit; Kiraci, Ali; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Raman shifts of the soft mode A(1g) and the B-1 mode are calculated at various pressures at room temperature for the cubic-tetragonal transition (P-c = 9.5 GPa) in SrTiO3. This calculation is performed using the observed volume data through the mode Gruneisen parameters of A(1g) and B-1 which vary with pressure, by fitting to the experimental wavenumbers in this crystalline system. Calculated Raman shifts are then used as order parameters to predict the pressure dependence of the damping constant and the inverse relaxation time for the cubic-tetragonal transition in SrTiO3. Our predictions from the pseudospin-phonon coupling and the energy fluctuation models can be compared with the experimental measurements when available in the literature.
Citation - WoS: 8
Citation - Scopus: 8
Damping Constant (Linewidth) and the Relaxation Time of the Brillouin La Mode for the Ferroelectric-Paraelectric Transition in Pbzr1-Xtixo3
(Ieee-inst Electrical Electronics Engineers inc, 2016) Kiraci, Ali; Yurtseven, Hamit; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The damping constant (linewidth) of the longitudinal acoustic (LA) mode is calculated as a function of temperature using the observed Brillouin frequencies of this mode from the literature for the ferroelectric-paraelectric transition (T-C = 657 K) in PbZr1-xTixO3 (x = 0.45). For this calculation of the damping constant, the pseudospin-phonon coupled model and the energy fluctuation model are used by fitting to the observed data for the Brillouin frequencies of the LA mode in the ferroelectric (T < T-C) and paraelectric (T > T-C) phases of this compound (x = 0.45). Values of the activation energy are deduced for both ferroelectric and paraelectric phases. The relaxation time is also obtained by means of fitting to the observed data from the literature for the inverse relaxation time at various temperatures in the paraelectric phase of PbZr1-xTixO3. The temperature dependences of the damping constant and of the relaxation time with the values of the activation energy that we have calculated indicate that the pseudospin-phonon coupled model and the energy fluctuation model are capable of describing the ferroelectric-paraelectric transition (T-C = 657 K) in PbZr1-xTixO3 (x = 0.45) adequately.
Citation - WoS: 3
The Important Role of N(2) Ion in the Phase-Transition Mechanism of [N(ch3)4]2znbr4
(Ieee-inst Electrical Electronics Engineers inc, 2020) Kiraci, Ali; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The chemical shift of the N(2)(CH3)(4) ion, which has been found to exhibit the similar anomalous behavior of the monoclinic angle $\Delta \beta $ , was related to the order parameter to evaluate the temperature dependence of the linewidth (damping constant) for N-14 nuclear magnetic resonance spectrum of this crystal in terms of the dynamic Ising models, namely the pseudospin-phonon-coupled (PS) and the energy fluctuation (EF) models. The results from both PS and EF models were successful to explain the abnormal behavior of the linewidth in the vicinity of the phase-transition temperature of ${T}_{C}= {287.6}$ K, when compared with the observed linewidth of the transverse acoustic soft mode in this crystal. As an extension of this work, the N-14 relaxation time and the values of the activation free energy were calculated as a function of temperature. The results indicate that the ferroelastic-paraelastic phase transition in this compound is of the order-disorder type.
Citation - WoS: 4
Citation - Scopus: 4
Order-Disorder Transition in the Ferroelectric Litao3
(Taylor & Francis Ltd, 2019) Yurtseven, Hamit; Kiraci, Ali; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The temperature dependences of the damping constant and the relaxation time are calculated by using the Raman frequencies of a* and the lowest A(1) (TO) phonons in the ferroelectric phase close to the ferroelectric-paraelectric transition in LiTaO3 (T-C = 963 K). Both calculations are performed by considering the frequency as an order parameter for the pseudospin-phonon (PS) and the energy fluctuation (EF) models using the observed data from the literature. Values of the activation energies of this crystal are also deduced by using both models in this crystal. Our results show that the PS and EF models can describe the observed behavior adequately for the order-disorder transition in LiTaO3.
Phenomenological Study of Lithium-Sodium Tetragermanate Close to the Phase Transition
(Springer Nature, 2025) Kiraci, Ali; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
This study presents an analysis of the dielectric and thermal properties in the vicinity of the second-order ferroelectric phase transition, with a specific emphasis on lithium-sodium tetragermanate, LiNaGe4O9. The power-law equation is employed by modifying the Kouvel-Fisher (KF) technique, which articulates the magnetization () and magnetic susceptibility in relation to the spontaneous polarization () and the dielectric constant () within ferroelectric frameworks. A parallel methodology is adopted to elucidate the heat capacity () and thermal expansivity () in the vicinity of phase transitions occurring in LiNaGe4O9. We demonstrate that the continuous fluctuations in and with temperature nearing the Curie point (TC108 K) as an indication of a second-order transition in LiNaGe4O9. Furthermore, a linear correlation is also established between and with temperature approaching the Curie point TC for this crystal structure. Experimental data are used from the literature for our analysis. Our findings show that the critical behavior of one dielectric or thermal property near the transition temperature in LiNaGe4O9 can be predicted from the other through these linear relationships. The methodology articulated herein for delineating the dielectric and thermal characteristics of LiNaGe4O9 close to the Curie point is extendable to various other ferroelectric materials. © 2025 Elsevier B.V., All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Phenomenological Study of Manganese Antimonite Close To the Neel Temperature
(Ieee-inst Electrical Electronics Engineers inc, 2021) Kiraci, Ali; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The anomalous behavior of the frequency f and specific heat C-p data for the new layered trigonal (P (3) over bar 1m) form of manganese antimonite (MnSb2O6) was analyzed by means of the power-law relations with the critical exponent alpha in the vicinity of the Neel temperature of T-N= 8.0 K. While the extracted values of a from both f and C-p below T-N (the same value of 0.06) match exactly the value 1/16 (= 0.06) predicted from the three-dimensional (3-D) Ising model, the extracted value of 0.65 from the C-p data above T-N is much higher than the predicted value of 1/8 (= 0.13) from the 3-D Ising model. As an extension of this work, the temperature dependence of the muon-spin relaxation rate (damping constant) lambda of MnSb2O6 was calculated from the pseudospin-phonon-coupled (PS) model and the energy fluctuation (EF) model below T-N. Our results are in good agreement with the data. In addition, the activation energy was calculated from the predicted values of. from both PS and EF models for MnSb2O6. Our results indicate an order-disorder-type transition at T-N = 8.0 K for MnSb2O6.
Pressure and Temperature Dependence of the Dielectric Properties in Barium Titanate
(Indian Academy of Sciences, 2025) Kiraci, Ali; Yurtseven, Hamit; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Temperature and pressure dependences of the soft-mode frequency (omega) and the dielectric constant (epsilon) are studied for the tetragonal-cubic transition (T-C = 395 K) in BaTiO3. We find that variations of the frequency and the dielectric constant with the temperature (pressure) are related to each other linearly close to the phase transition in this ferroelectric material. Instead of the Curie-Weiss behaviour of the dielectric constant, the critical behaviour of both soft-mode frequency and the dielectric constant is expressed by the power-law formulae, and the critical exponents are determined using the observed data from the literature. Our predicted frequencies of the soft mode at various pressures and temperatures, can be examined by the experimental measurements close to the tetragonal-cubic transition in BaTiO3.
Citation - WoS: 1
Citation - Scopus: 1
Pressure Dependence of the Raman Frequency Calculated From the Volume Data Close To the Ferroelectric-Paraelectric Transition in Pbtio3
(Taylor & Francis Ltd, 2017) Kiraci, Ali; Yurtseven, Hamit; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
We calculate the pressure dependence of the Raman frequencies of some Raman modes by using the observed volume data through the mode Gruneisen parameters for the ferroelectri-paraelectric transition in PbTiO3. The mode Gruneisen parameters which we have determined using the observed Raman frequencies for the soft modes, increase considerably with increasing pressure toward the transition pressure (PC similar to 11 GPa) from the tetragonal (ferroelectric) to the cubic (paraelectric) phase in PbTiO3. Variation of the mode Gruneisen parameter with the pressure is rather smooth for the other Raman modes studied as compared to the drastic change at PC for the soft modes in this ferroelectric material. Raman frequencies (energy shifts) of the modes which we have calculated, decrease from the ferroelectric to the paraelectric phase with the exception of the optical modes of E(3LO) and E(3TO) whose Raman frequencies increase with increasing pressure. This decrease and/or increase in the energy shifts for the Raman modes which we have calculated as also observed experimentally, shows a continuous manner, indicating a second order character rather that the first order transition from the tetragonal to the cubic phase in PbTiO3.
Citation - WoS: 6
Citation - Scopus: 5
Pressure-Dependent Raman Modes Near the Cubic-Tetragonal Transition in Strontium Titanate
(Wiley, 2018) Yurtseven, Hamit; Kiraci, Ali; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The pressure dependence of the Raman frequency shifts of various Raman modes is calculated at room temperature using the volume data from the literature for the cubic-tetragonal transition in SrTiO3. The isothermal mode Gruneisen parameters of those Raman modes are obtained, which decrease with increasing pressure for this molecular crystal. Calculated Raman frequencies are then used to predict the damping constant and the inverse relaxation time of those Raman modes as a function of pressure by means of the pseudospin-phonon (PS) coupled model and the energy fluctuation (EF) model to describe the cubic-tetragonal transition in SrTiO3. Also, the values of the activation energy are extracted for the Raman modes studied using both models (PS and EF). Our predicted damping constant and the inverse relaxation time for the Raman modes, can be compared with the experimental measurements close to the cubic-tetragonal transition in SrTiO3.
Citation - WoS: 1
Citation - Scopus: 2
Thermodynamic and Dielectric Properties of Hexagonal Barium Titanate Near the Phase Transitions
(Iop Publishing Ltd, 2024) Yurtseven, Hamit; Kiraci, Ali; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The critical behavior of the thermodynamic quantities is studied for the two phase transitions near the transition temperatures (74 K and 222 K) in the hexagonal (h) BaTiO3. A linear relationship has been established between the variations of the frequency shifts and of the dielectric constant by using the literature data in h-BaTiO3. Temperature and pressure dependence of the mode Gr & uuml;neisen parameters ( gamma p and gamma T ) are also described by a power-law formula as the other thermodynamic parameters near Tpt in h-BaTiO3. Our results show that they explain the observed behavior adequately, in particular soft-mode frequency, dielectric constant, thermal expansion, the excess specific heat and the entropy near Tpt in h-BaTiO3. Temperature dependence of the isobaric mode Gr & uuml;neisen parameter ( gamma p ), enthalpy and the Gibbs free energy, which we have evaluated, can be compared with experiments in h-BaTiO3.
A Thermodynamic Study on Pbzr0.52ti0.48o3 Ceramic Close To the Tetragonal-Cubic Transition
(Springer, 2020) Kiraci, Ali; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The isobaric Gruneisen parameter and the wavenumber (frequency) of various Raman modes in PbZr1-xTixO3 (PZT x = 0.48) ceramic were calculated by means of the unit cell volume of this crystal. In addition, the damping constant (linewidth) of the Raman modes studied was computed from the pseudospin-phonon coupled and from the energy fluctuation models close to the tetragonal-cubic transition temperature of T-C = 650 K. This calculation of the damping constant performed in terms of the order parameter (spontaneous polarization), which was associated with the wavenumbers of the Raman modes studied. Furthermore, the inverse relaxation time of the Raman modes in this ceramic calculated and the values of the activation energy were deduced in terms of the Arrhenius plot close to the tetragonal-cubic transition in PZT (x = 0.48) ceramic. Finally, the temperature dependence of some thermodynamic quantities, such as the isothermal compressibility and the specific heat of this ceramic, was predicted.