Hydrostatic Pressure Influence on Phase Transition and Physical Properties of Kd_{2}po_{4}-Type Ferroelectrics

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.

Section: Discussionmentioning

confidence: 86%

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

“…This is another evidence for the weakness of the tunnelling model for all-round description of pressure effects in KDP-type crystals. It has been shown in a number of papers [14][15][16][17][18] that an essential improvement of the theoretical description of the wide variety of the experimental data concerning the pressure effect on the physical properties of KDP-type crystals can be achieved with the account of short-range configurational interactions. Therefore, it seems important to perform further theoretical studies of the specific features of the temperature behaviour of longitudinal ε c and transverse ε a dielectric permeability in KDP-type crystals under external pressure, namely to analyze the obtained results in the framework of the proton ordering model with the account of short-range and long-range interactions and proton tunnelling at hydrogenic bonds in the four-particle cluster approximation [19,20].…”

Section: Resultsmentioning

confidence: 99%

Temperature and Pressure Effect on the Anisotropy of Dielectric Permeability in KDP and DKDP Crystals

Kedyulich¹,

Slivka²,

Gerzanich³

et al. 2003

Temperature dependences of longitudinal and transverse dielectric permeability of KDP and DKDP crystals are studied at different values of hydrostatic pressure in order to determine the pressure behaviour of the isotropic point for these crystals. The isotropic point temperature in KDP crystals at atmospheric pressure is T i = 186 K at the measuring field frequency 1 kHz and T i = 176 K at the frequency of 1 MHz. In DKDP crystals the isotropic point is achieved at the temperature T i = 300 K ( 1 kHz) and T i = 253 K ( 1 MHz). The hydrostatic pressure increase results in the reduction of the isotropic point temperature with the pressure coefficients ∂T i /∂p = −4.3 K/kbar for KDP and ∂T i /∂p = −2.9 K/kbar for DKDP. The analysis of the experimental results in the framework of the Blinc-Žekš pseudospin formalism has shown a good agreement between the calculated and the experimentally obtained temperature of the isotropic point for KDP crystals.

“…of the deuterated members of the family. Later, a microscopic theory of deformed deuterated crystals of this type was developed [63], within which a proper description of pressure and electric field effects on their physical characteristics was obtained [59][60][61][62]. Essential point in the theoretical studies was a development of the wellgrounded fitting procedure; especially we would like to mention the papers [29][30][31], where it was shown that in the fitting it is important to have reliable experimental data for the specific heat of the crystals.…”

Section: Discussionmentioning

confidence: 99%

Isotopic Effects in Partially Deuterated Piezoelectric Crystals of Rochelle Salt

Levitskii¹,

Zachek²,

Moina³

et al. 2004

We develop a theory for dielectric, piezoelectric, and elastic properties of partially deuterated (quenched disorder) crystals of Rochelle salt with taking into account the piezoelectric coupling. Results of numerical calculations are presented for a completely deuterated Rochelle salt and compared with available experimental data. Isotopic effect is explored within the mean crystal approximation, as well as within the developed theory using different trial sets of the fitting parameters. Theory predictions are given for the temperature and composition dependences of the calculated characteristics for partially deuterated crystals.