Browsing by Author "Kiraci, A."

Now showing 1 - 18 of 18

Citation - WoS: 3
Citation - Scopus: 3
A phenomenological study on ferroelastic KH3(SeO3)(2) and KD3(SeO3)(2)
(Pergamon-elsevier Science Ltd, 2021) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
The anomalous behavior of the Brillouin frequency shift omega of the soft acoustic mode for KH3(SeO3)(2) and KD3(SeO3)(2), and also the volume thermal expansion proportional to(V) and the specific heat C of KH3(SeO3)(2) have been analyzed for various temperature intervals close to the phase transition temperatures TC at around 211 K and 302 K, respectively. Our extracted values of the critical exponent from C and proportional to(V) of KH3(SeO3)(2) within the temperature intervals of vertical bar T -T-C vertical bar < 7 K are nearly zero, while the critical exponent extracted from the Brillouin frequency shift data of both KH3(SeO3)(2) and KD3(SeO3)(2) within the same temperature interval of vertical bar T -T-C vertical bar < 7 K decrease very rapidly toward to zero as the phase transition temperatures are approached. Our results indicate that the critical behavior of omega, proportional to(V) and C of both KH3(SeO3)(2) and KD3(SeO3)(2) can be described with the same critical exponent within the temperature interval of vertical bar T -T-C vertical bar < 2 K.
Citation - WoS: 6
Citation - Scopus: 6
A phenomenological study on ferroelectric pyridinium tetrafluoroborate (C5NH6) BF4
(Elsevier, 2019) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
The temperature dependence of the specific heat C-V of (C5NH6)BF4 was analyzed according to a power law formula with a critical exponent alpha deduced from the compressible Ising model in the vicinity of the phase transition temperatures of T-C1 = 238 K and T-C2 = 204 K. The extracted values of the critical exponent alpha within the temperature intervals of vertical bar T - T-C1 vertical bar < 6 K and also T - T-C2 < 6 K were consistent with that predicted from the 3d-Ising model (alpha = 0.10) while obtained values of alpha within the temperature interval of T-C2 - T < 6 K were consistent with that predicted from 2-d potts model (alpha = 0.30). In addition, the thermodynamic quantities: the internal energy (U), the entropy (S) and the Helmholtz free energy (F) of this compound were calculated on the basis of the extracted values of the critical exponent a below and above the phase transition temperatures of T-C1 and T-C2.
Citation - WoS: 2
Citation - Scopus: 3
A phenomenological study on ferroelectric β-glycine
(Taylor & Francis Ltd, 2021) Kiraci, A.; 42475
The anomalous behavior of the specific heat for beta-glycine was analyzed in terms of the compressible Ising model approximately 5 K below and above the ferrelectric-paraelectric phase transition temperature of T-C =252 K. The obtained value of the critical exponent alpha =0.12 in the ferroelectric phase (T < TC) was consistent with that predicted from the 3-d Ising model (alpha =0.13), while the obtained value of alpha =0.32 in the paraelectric phase (T > TC) was consistent with that predicted from the 2-d potts model (alpha =0.30). Some thermodynamic quantities such as the internal energy, the entropy and the free energy of beta-glycine were then predicted in terms of these extracted values of the critical exponents close to the phase transition temperature of TC. Our calculated values of the thermodynamic quantities are in good agreement with the observed data.
Citation - WoS: 0
Citation - Scopus: 0
Analysis and mathematical computation of some dynamic functions for the guanidine zinc sulfate
(Taylor & Francis Ltd, 2021) Askun, A. R.; Kiraci, A.; 56475
A power-law formula with a critical exponent alpha was used to analyze the anomalous behavior of the specific heat for guanidine zinc sulfate (GZS) crystal close to the phase transition temperature of T-c = 178.4 K. The obtained values of 0.13 and 0.14 for alpha below (T < T-c) and above (T> T-c) the phase transition temperature, respectively, were almost the same value of 0.13 (1/8) that predicted from the 3-D (sing model. Also, the internal energy U, the entropy S and the free energy G of this crystal were calculated as a function of temperature dose to the phase transition temperature of T-c = 178.4 K.
Citation - WoS: 0
Citation - Scopus: 0
Analysis of the specific heat and the free energy and calculation of the entropy and the internal energy of [N(CH3)(4)](2)MnBr4 close to the phase transition
(Taylor & Francis Ltd, 2021) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
The critical behavior of the specific heat and the Gibbs free energy of [N(CH3)(4)](2)MnBr4 was analyzed using the 'sing model close to the phase transition temperature of T-c = 276.5 K. Obtained value of alpha=0.02 from the Gibbs free energy and from the specific heat approximately 2.0 K and 1.4 K, respectively, below Tc (ferroelastic phase) and also deduced value of alpha= 0.04 from the specific heat approximately 0.3 K above T-c (paraelastic phase) can be compared with that predicted from mean field theory (alpha = 0). Also, the entropy and the internal energy of this crystal were predicted.
Citation - WoS: 8
Citation - Scopus: 8
Analysis of the specific heat and the free energy of [N(CH3)(4)](2)ZnBr4 close to the ferro-paraelastic phase transition
(Taylor & Francis Ltd, 2019) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
A power-law formula deduced from the Ising model was used to analyze the temperature dependence of the specific heat and the Gibbs free energy of [N(CH3)(4)](2)ZnBr4 compound in the vicinity of the phase transition temperature of T-C = 287.2 K. Obtained values of the critical exponents from the Gibbs free energy were consistent with that predicted from 2-d potts model ( = 0.3), while obtained values of from the specific heat in both ferroelastic and paraelastic phases were consistent with that predicted from the mean field theory ( = 0) in the vicinity of the phase transition temperature. This is an indication of that [N(CH3)(4)](2)ZnBr4 compound undergoes a second order type phase transition. Also, the enthalpy () and the entropy () of this crystal were calculated in terms of the extracted values of the critical exponent in both ferroelastic and paraelastic phases.
Citation - Scopus: 0
Calculation of the Halfwidth and the Activation Energy for the Soft Raman Modes in the Brominated Compounds of Tris-Sarcosine Calcium Chloride
(Walailak University, 2022) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
This letter contributes how to calculate the anomalous behavior for the damping constant (halfwidth) of the ferroelectric Tris-Sarcosine Calcium Chloride (TSSC) and its brominated compounds TSSC1−xBrx (x = 0.13, 0.42 and 0.60) from the wavenumber data of the soft modes below the phase transition temperature of TC. The pseudospin-phonon coupled (PS) and the energy fluctuation (EF) models derived from the dynamical Ising model were used. Both PS and EF models have been used to contribute understanding the temperature dependence of the phase transition mechanism of TSSC1−xBrx. In addition, values of the activation energy for TSSC1−xBrx (x = 0, 0.13, 0.42 and 0.60) were extracted from the damping constant as calculated from both models (PS and EF). Our results indicate order-disorder type phase transition for TSSC1−xBrx. © 2022, Walailak University. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 2
Calculation of the infrared frequencies as a function oftemperature using the volume data in the ferroelectric phase ofnano2
(Taylor & Francis Ltd, 2014) Yurtseven, H.; Kiracı, Ali; Kiraci, A.; 42475; Ortak Dersler Bölümü
We calculate the temperature dependence of the infrared frequencies of the TO and LO modes with the symmetries of A(1), B-1 and B-2 mainly in the ferroelectric phase of NaNO2. This calculation is carried out using the volume dependence of the infrared frequencies through the mode Gruneisen parameter in this crystal. The volume dependences of the infrared frequencies are fitted to the observed frequencies by using constant mode Gruneisen parameter in the ferroelectric phase of NaNO2. Our results show that this method of calculating the infrared frequencies describes the observed behaviour of NaNO2 adequately.
Citation - WoS: 4
Citation - Scopus: 5
Calculation of the raman frequency, damping constant (Linewidth) and the relaxation time near the tetragonal-cubic transition in PbTiO3
(Elsevier Gmbh, 2017) Kiraci, A.; Kiracı, Ali; Yurtseven, H.; 42475; Ortak Dersler Bölümü
Frequencies, damping constants and the relaxation times of some Raman modes including the two soft modes are calculated as a function of pressure near the tetragonal-cubic transition in PbTiO3. Calculation of the Raman frequencies is performed using the observed volume data from the literature by means of the mode Gruneisen parameter at various pressures. Pressure dependence of the damping constant and the relaxation time is predicted using the pseudospin-phonon coupled model and the energy fluctuation model by considering that the Raman frequency can be taken as the order parameter (spontaneous polarization) for the tetragonal-cubic transition in PbTiO3. Expressions from both models for the damping constants are fitted to the observed Raman linewidths of the two soft modes and for the other Raman modes the damping constant and the relaxation time are predicted close to the transition. We find that damping constants diverge and the inverse relaxation time decreases for the soft modes with increasing pressure near the critical pressure (P-c similar to 11 GPa). The other Raman modes exhibit unusual critical behavior. Our results indicate that the observed behavior of the Raman frequencies can be predicted from the volume data through the mode Gruneisen parameter for the tetragonal-cubic transition in PbTiO3. The damping constant and the relaxation time for the Raman modes can also be predicted adequately using the pseudospin-phonon coupled model and the energy fluctuation model to explain the mechanism of the phase transition between the tetragonal and cubic phases in PbTiO3. (C) 2017 Elsevier GmbH. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
Calculation of the spin-lattice relaxation time and the activation energy near the IV–III phase transition in pyridinium fluorosulfonate (C5NH6)FSO3
(Taylor & Francis Ltd, 2022) Kara, N.; Kiraci, A.; Yurtseven, Hamit; 42475
The spin-lattice relaxation time T-1(H) for protons nuclei is calculated in term of the pseudospin-phonon (PS) coupled and the energy fluctuation (EF) models close to the IV-III solid-solid phase transition of T-C = 235 K in (C5NH6)FSO3. This calculation was performed by associating the observed second moment of the H-1 as the order parameter below k and the disorder parameter above T-C. Values of the activation energy for the cation reorientation in this crystal are also deduced by using both models. In addition, the observed dielectric permittivity of this crystal is analyzed within the framework of the Landau theory and values of the spontaneous polarization (P-s) are determined as a function of temperature. The normalized values of P-s are used in the PS and EF models to extract the activation energy for the reorientation of the dipole moment of this compound arising from cation-anion interaction. Our results show that the PS and EF models can describe the observed behavior of the spin-lattice relaxation time adequately for the IV-III solid-solid transition in (C5NH6)FSO3.
Citation - WoS: 3
Citation - Scopus: 4
Damping constant and the inverse relaxation time calculated as a function of pressure using the X-ray diffraction data close to the cubic-tetragonal phase transition in SrTiO3
(Taylor & Francis Ltd, 2019) Yurtseven, H.; Kiracı, Ali; Kiraci, A.; 42475; Ortak Dersler Bölümü
The damping constant is calculated as a function of pressure at room temperature using the normalized intensity as an order parameter near the cubic-tetragonal phase transition in SrTiO3. The observed X-ray diffraction data are used for the normalized intensities to calculate the damping constant () from the pseudospin-phonon (PS) coupled model and the energy fluctuation (EF) model, which is fitted to the observed FWHM data from the literature for comparison. Using the calculated values, the pressure dependence of the inverse relaxation time () is predicted close to the cubic-tetragonal phase transition in SrTiO3. Our calculated damping constant from both models explains the observed FWHM satisfactorily and our prediction of the inverse relaxation time can also be compared with the experimental measurements when they are available in the literature.
Citation - WoS: 7
Citation - Scopus: 8
Damping constant and the relaxation time calculated for the lowest-frequency soft mode in the ferroelectric phase of Cd2Nb2O7
(Elsevier Gmbh, Urban & Fischer verlag, 2016) Kiraci, A.; Kiracı, Ali; Yurtseven, H.; 42475; Ortak Dersler Bölümü
The temperature dependence of the phonon frequency omega(ph) and of the damping constant Gamma(sp) due to pseudospin-phonon coupling of the lowest-frequency soft mode is calculated in the ferroelectric phase near the transition temperature (T-C =196 K) in Cd2Nb2O7. Raman frequency of the soft mode is used as an order parameter which is calculated from the molecular field theory. On that basis, the damping constant is calculated by fitting the expressions from the pseudospin-phonon coupled model and the energy fluctuation model to the observed linewidth from the literature below T-C in Cd2Nb2O7. From our analysis, we find that the molecular field theory is adequate for the soft mode behaviour and that both models are also satisfactory for the divergence behaviour of the damping constant as T-C is approached from the ferroelectric phase in Cd2Nb2O7. Values of the activation energy U are extracted from the temperature dependence of the damping constant (HWHM) of the soft mode in the ferroelectric phase of this crystal. Also, the inverse relaxation time is predicted using the Raman frequency and damping constant close to the T-C in the ferroelectric phase of Cd2Nb2O7, which increases considerably as T-C is approached from the ferroelectric phase, as observed experimentally. (C) 2016 Elsevier GmbH. All rights reserved.
Citation - WoS: 0
Citation - Scopus: 0
Investigation of the anomalous behavior of the linewidth (damping constant) for the Raman Ag modes in SrSnO3 ceramic
(Taylor & Francis Ltd, 2022) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
The anomalous behavior of the linewidth (damping constant) for the Raman A(g) modes of 223 cm(-1) and 260 cm(-1) that contribute to the phase transition mechanism of SrSnO3 ceramic close to the phase transition temperatures of T-C1= 650 K and T-C2= 530 K, respectively, was calculated as function of temperature from the pseudospin-phonon coupled (PS) and the energy fluctuation (EF) models below (T < T-C) and above (T > T-C) the phase transition temperatures of T-C1 and T-C2. For this calculation, the frequency shift of these modes were associated as the order parameter and disorder parameter below and above T-C, respectively. Our results are in good agreement with the observed linewidth of these 223 cm(-1) and 260 cm(-1) Raman A(g) modes. In addition, these two models (PS and EF) were used to deduce the values of the activation energy for SrSnO3 ceramic below and above the phase transition temperatures of T-C1 and T-C2.
Citation - WoS: 0
Citation - Scopus: 1
Phenomenological approaches on the Nd3+ doped ferroelectric LaBGeO5
(Taylor & Francis Ltd, 2021) Kara, N.; Kiracı, Ali; Kiraci, A.; Yurtseven, Hamit; Ortak Dersler Bölümü
Two phenomenological models, namely the compressible Ising model and Landau model, have been used to analyze the specific heat and the dielectric constant data, respectively for the pure and Nd3+ doped LaBGeO5 (LBG) crystals. The critical exponent of the specific heat was extracted in both ferroelectric and paraelectric phases of the crystals studied here within the temperature intervals of [T - T-C vertical bar < 4 K. The extracted values of the critical exponent were then used to predict some thermodynamic quantities such as the enthalpy, entropy, and the Gibbs free energy. Regarding the analysis of dielectric constant data within the framework of the Landau theory, the observed values of the birefringence were associated with the order parameter below the transition temperature T-c. The Landau coefficients a(0) and a(4) were determined. Our results indicate a second-order phase transition mechanism.
Citation - WoS: 0
Citation - Scopus: 0
Raman wavenumbers calculated as a function of pressure from the mode Gruneisen parameter of PZT (x=0.48) ceramic close to the monoclinic-cubic transition
(World Scientific Publ Co Pte Ltd, 2019) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
The isothermal mode Gruneisen parameter gamma(T)(P) of some Raman modes in PbZr1-xTixO3 (PZT, x = 0.48) were calculated as a function of pressure by means of the observed pressure-dependent volume data of PZT (x = 0.48) crystal from the literature at room temperature of 298 K. Those calculated values of gamma(T)(P) were then used to compute the pressure dependence of the Raman modes in PZT (x = 0.48) ceramic studied here. The observed and calculated values of the Raman wavenumbers in PZT were in good agreement, which indicates that the isothermal mode Gruneisen parameter can also be used to predict the pressure-dependent wavenumbers of some other perovskite-type crystals. Additionally, the pressure dependence of the thermodynamic quantities such as isothermal compressibility kappa(T), thermal expansion alpha(P) and the specific heat C-P - C-V of PZT (x = 0.48) ceramic were predicted at constant temperature of 298 K. Here, the experimentally measurable thermodynamic quantities calculated for PZT (x = 0.48) ceramics provide theoretically a significant opportunity for testing.
Citation - WoS: 5
Citation - Scopus: 3
Temperature Dependence of the Brillouin Frequency Shift and the Linewidth of the La Mode in the Ferroelectric Phase of Pzt-X (pbzr1-Xtixo3)
(Ieee, 2015) Yurtseven, F.; Korkmaz, C. Sisman; Kiraci, A.
The temperature dependence of the Brillouin frequency and the linewidth of the LA mode is studied for the concentration of x=0.45 in the ferroelectric phase of PbZr1-xTixO3 (PZT-x) within the temperature range of 443 to 656 K (T-C=657 K). Using the experimental data for the Brillouin frequency of the LA mode as an order parameter below T-C the temperature dependence of the linewidth (FWHM) is calculated by the pseudospin-phonon coupled model and the energy fluctuation model for the lead titanate zirconate (x=0.45). Additionally, the activation energies are compared from the damping constant (linewidth) using both models for the temperature range of 443 to 656 K in the ferroelectric phase of PbZr1-xTixO3. Our calculated values for the damping constant are in agreement with the observed data for the ferroelectric phase of PbZr1-xTixO3 single crystals. The activation energies calculated from both models are much higher in the ferroelectric phase than the value of k(B)T(C)=0.056 eV at the transition temperature for PbZr1-xTixO3 (x=0.45).
Citation - WoS: 9
Citation - Scopus: 10
Temperature dependence of the damping constant and the relaxation time close to the tetragonal-cubic phase transition in SrZrO3
(Elsevier Science Bv, 2017) Yurtseven, H.; Kiracı, Ali; Kiraci, A.; 42475; Ortak Dersler Bölümü
The damping constant Gamma(sp) due to the pseudospin-phonon coupling is calculated as a function of temperature using the pseudospin-phonon coupled model and the energy fluctuation model close to the tetragonal-cubic transition (T-C = 1443 K) in SrZrO3. Using the observed Raman frequencies and the linewidth (FWHM) of the soft modes (E-g and A(1g)) from the literature, predictions of both models studied, are examined for the tetragonal-cubic transition in this crystalline system. Values of the activation energy U are extracted and also the inverse relaxation time is predicted as a function of temperature close to the phase transition studied in SrZrO3. Divergence behaviour of the damping constant (FWHM) of the soft modes is predicted from both models as also observed experimentally when T-C is approached from the tetragonal to the cubic phase in SrZrO3. The relaxation time also diverges close to the T-C in this crystal. It is indicated that the tetragonal cubic transition is of a second order as predicted from both models studied here, as also observed experimentally in SrZrO3. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Temperature dependence of the polarization, dielectric constant, damping constant and the relaxation time close to the ferroelectric-paraelectric phase transition in LiNbO3
(Elsevier Gmbh, Urban & Fischer verlag, 2017) Kiraci, A.; Kiracı, Ali; Yurtseven, H.; 42475; Ortak Dersler Bölümü
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 data from the literature. The temperature dependences of the damping constant and the inverse relaxation time are also computed using the pseudospin-phonon coupled model and the energy fluctuation model for the ferroelectric phase of LiNbO3. The activation energy is deduced from the damping constant for both models studied and compared with the k(B)T(C) value of LiNbO3. We find that the order parameter (Raman frequency of the TO1 mode) and the inverse dielectric susceptibility decrease with increasing temperature, as expected from the mean field model. We also find that the damping constant and the inverse relaxation time of this soft mode increases and decreases, respectively, with increasing temperature on the basis of the two models studied in the ferroelectric phase of LiNbO3. This indicates that our method of calculation is satisfactory to describe the observed behaviour of the ferroelectric-paraelectric phase transition in LiNbO3. (C) 2016 Elsevier GmbH. All rights reserved.