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Analysis of the Specific Heat and the Free Energy and Calculation of the Entropy and the Internal Energy of [N(ch3)4]2mnbr4 Close To the Phase Transition
(Taylor & Francis Ltd, 2021) Kiraci, A.
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]2znbr4 Close To the Ferro-Paraelastic Phase Transition
(Taylor & Francis Ltd, 2019) Kiraci, A.
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.
Investigation of the Anomalous Behavior of the Linewidth (Damping Constant) for the Raman Ag Modes in Srsno3 Ceramic
(Taylor & Francis Ltd, 2022) Kiraci, A.
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: 3
Citation - Scopus: 3
A Phenomenological Study on Ferroelastic Kh3(Seo3)2 and Kd3(Seo3)2
(Pergamon-elsevier Science Ltd, 2021) Kiraci, A.
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.
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.
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.
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.
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.

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