Correlation functions of quenched and annealed Ising systems

A system of equations for the averaged phonon Green function determining the shapes of the lines in Raman scattering spectra is obtained in the coherent potential approximation. Configurationally split components of the Raman scattering are studied within a simple model. For the KH 2 PO 4 and the CsH 2 PO 4 -type ferroelectrics the possibility to observe the configurational splitting experimentally is discussed.

Section: Appendixsupporting

confidence: 90%

“…It was shown in [10] that the description of the Raman spectra of internal oscillations in KH 2 PO 4 clusters can be made if different realizations of proton configurations are taken into account. The model can easily be extended to allow for the short-range proton correlations [11].…”

Section: Introductionmentioning

confidence: 99%

Configurational Splitting in Raman Scattering Spectra of Crystals With the Order-Disorder Type Phase Transitions

Stasyuk¹,

Ivankiv²

1999

“…In [69] the role of the longrange dipole-dipole interactions in the phase transitions in these crystals and their effect on the spontaneous strain and polarization were explored. The fourth-order phonon anharmonisms were added to the pseudospin-phonon model of hydrogen bonded ferroelectrics (see e. g. [70][71][72][73]), but their role in the KH 2 PO 4 type crystals has not been completely clarified, because of the essential short-range correlations neglected in these models.…”

Section: Introductionmentioning

confidence: 99%

“…In the papers of the first sector, the models of ferroelectric hydrogen bonded compounds (also of the orthophosphates), were explored using the Green's functions method with different methods of decoupling of the equation chain for them [60][61][62][63][64][65][66][67][68][71][72][73][74][75][77][78][79][80][81][82][83][84][85][86] and diagram method for the Matsubara Green's functions (see [62,[87][88][89][90][91][92][93]) used. In [94] within the functional integration method (see [95]), free energy and Green's functions of a simple proton-ionic model of hydrogen bonded ferroelectrics were calculated.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics and dynamical properties of the KH_{2}PO_{4} type ferroelectric compounds. A unified model

Levitskii¹,

Zachek²,

Vdovych³

et al. 2009

Within the framework of the proposed unified proton ordering model for the ferroelectric compounds of the KH 2 PO 4 family, in the four-particle cluster approximation for the short-range interactions and mean field approximation for the long-range interactions, we calculate thermodynamic and longitudinal dynamic characteristics of the KD 2 PO 4 type ferroelectrics and ND 4 D 2 PO 4 type antiferroelectrics. Calculations for partially deuterated K(H 1−x Dx) 2 PO 4 type ferroelectrics and N(H 1−x Dx) 4 (H 1−x Dx) 2 PO 4 type antiferroelectrics are performed within the mean crystal approximation. It is shown that at the proper choice of the theory parameters, a good quantitative description of experimental data for the KH 2 PO 4 family crystals is obtained.

“…Theoretic studies of the K(H 1−x D x ) 2 PO 4 crystals ware carried out in the works [1][2][3][4][5][6][7][8][9][10][11][12]. All studies of the mixed K(H 1−x D x ) 2 PO 4 ferroelectrics were carried out within one of the modifications of the proton ordering model or within the proton-phonon model.…”

Section: Introductionmentioning

confidence: 99%

Theoretical investigations of thermodynamic properties of partially deuterated K(H_{1-x}D_{x})_{2}PO_{4} ferroelectrics

Levitskii¹,

Lisnii²,

Andrusyk³

2007

The research of thermodynamic properties of partially deuterated K(H 1−x Dx) 2 PO 4 crystals was performed within the framework of proton ordering model with tunnelling within the four-particle cluster approximation for short-range interaction and within the molecular field approximation for long-range interaction. The KD 2 PO 4 's model parameters were derived for the case of acceptable description of the experimental data for crystal thermodynamic characteristics. Based on the introduced procedure of deriving parameters for K(H 1−x Dx) 2 PO 4 crystals, the thermodynamic and dielectric properties of these crystals were calculated and the results were compared with the experimental ones. The problem of applying the mean crystal approximation to the analysis of physical characteristics of K(H 1−x Dx) 2 PO 4 crystals was discussed.