Fizik Bilim Dalı

Analysis of the Specific Heat and the Free Energy of [N(Ch 3 ) 4 ] 2 Znbr 4 Close to the Ferro-Paraelastic Phase Transition

2020-07-03T10:59:17Z

Analysis of the Specific Heat and the Free Energy of [N(Ch 3 ) 4 ] 2 Znbr 4 Close to the Ferro-Paraelastic Phase Transition Kiracı, Ali A power-law formula deduced from the Ising model was used to analyze the temperature dependence of the specific heat C p and the Gibbs free energy G of [N(CH 3 ) 4 ] 2 ZnBr 4 compound in the vicinity of the phase transition temperature of T C = 287.2 K. Obtained values of the critical exponents α from the Gibbs free energy were consistent with that predicted from 2-d potts model (α = 0.3), while obtained values of α from the specific heat in both ferroelastic and paraelastic phases were consistent with that predicted from the mean field theory (α = 0) in the vicinity of the phase transition temperature. This is an indication of that [N(CH 3 ) 4 ] 2 ZnBr 4 compound undergoes a second order type phase transition. Also, the enthalpy (H) and the entropy (S) of this crystal were calculated in terms of the extracted values of the critical exponent in both ferroelastic and paraelastic phases.

A Thermodynamic Study On Pbzr0.52Ti0.48O3 Ceramic Close to the Tetragonal-Cubic Transition

2020-06-02T07:00:55Z

A Thermodynamic Study On Pbzr0.52Ti0.48O3 Ceramic Close to the Tetragonal-Cubic Transition Kiracı, Ali The isobaric Grüneisen 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 TC = 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.

Calculation of the infrared frequencies as a function oftemperature using the volume data in the ferroelectric phase ofnano2

2020-07-03T11:01:40Z

Calculation of the infrared frequencies as a function oftemperature using the volume data in the ferroelectric phase ofnano2 Yurtseven, H.; Kiracı, Ali 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.

Damping Constant (Linewidth) and the Relaxation Time of the Brillouin LA Mode for the Ferroelectric-Paraelectric Transition in PbZr1-xTixO3

2020-06-26T12:43:15Z

Damping Constant (Linewidth) and the Relaxation Time of the Brillouin LA Mode for the Ferroelectric-Paraelectric Transition in PbZr1-xTixO3 Yurtseven, Hamit; Kiracı, Ali 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.