Fizik Bilim Dalı Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/4363

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A phenomenological study on ferroelastic KH3(SeO3)(2) and KD3(SeO3)(2)
(2021) Kiracı, Ali; 42475
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.
A phenomenological study on ferroelectric β-glycine
(2021) Kiracı, A; 42475
The anomalous behavior of the specific heat for (Formula presented.) -glycine was analyzed in terms of the compressible Ising model approximately 5 K below and above the ferrelectric-paraelectric phase transition temperature of TC = 252 K. The obtained value of the critical exponent (Formula presented.) = 0.12 in the ferroelectric phase (T < TC) was consistent with that predicted from the 3-d Ising model ((Formula presented.) = 0.13), while the obtained value of (Formula presented.) = 0.32 in the paraelectric phase (T > TC) was consistent with that predicted from the 2-d potts model ((Formula presented.) = 0.30). Some thermodynamic quantities such as the internal energy, the entropy and the free energy of (Formula presented.) -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.
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
(2021) Kiracı, Ali; 42475
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.
Analysis of the specific heat and the free energy of [N(CH3)(4)](2)ZnBr4 close to the ferro-paraelastic phase transition
(2019) Kiracı, Ali; 42475
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.
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
(2019) Kiracı, Ali; Kiracı, Ali; 42475
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.
Investigation of the anomalous behavior of the linewidth (damping constant) for the Raman Ag modes in SrSnO3 ceramic
(2022) Kiracı, Ali; 42475
The anomalous behavior of the linewidth (damping constant) for the Raman Ag 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 TC1= 650 K and TC2= 530 K, respectively, was calculated as function of temperature from the pseudospin-phonon coupled (PS) and the energy fluctuation (EF) models below (T < TC) and above (T > TC) the phase transition temperatures of TC1 and TC2. For this calculation, the frequency shift of these modes were associated as the order parameter and disorder parameter below and above TC, respectively. Our results are in good agreement with the observed linewidth of these 223 cm−1 and 260 cm−1 Raman Ag 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 TC1 and TC2.
Order-disorder transition in the ferroelectric LiTaO3
(2019) Kiracı, Ali; Yurtseven, Hamit; 42475
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.
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
(2019) Kiracı, Ali; 42475
The isothermal mode Grüneisen parameter γT(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 298K. Those calculated values of γT(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 Grüneisen 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 κT, thermal expansion αP and the specific heat CP-CV of PZT (x=0.48) ceramic were predicted at constant temperature of 298K. Here, the experimentally measurable thermodynamic quantities calculated for PZT (x=0.48) ceramics provide theoretically a significant opportunity for testing.

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