COEXISTENCE OF PARAELECTRIC/PROTON-GLASS AND FERROELECTRIC (ANTIFERROELECTRIC) ORDERS IN Rb_{1-x}(NH_{4})_{x}H_{2}AsO_{4} CRYSTALS

We propose a pseudospin model for proton glasses of the Rb 1−x (NH 4 )xH 2 PO 4 (Rb 1−x (ND 4 )xD 2 PO 4 ) type, which takes into account the energy levels of hydrogens (deuterons) around the PO 4 group, long-range interactions between the hydrogen bonds, and an internal random deformational field. Within the framework of a cluster approximation and a mean field approximation over the long-range interactions, we derive a system of equations for the state parameters for the regions which are in the ferroelectric and antiferroelectric states, as well as in the proton glass state. Within the Glauber dynamics approach, we obtain a system of equations for the frequency-dependent linear responses of polarization and the proton glass order parameter. We obtain a qualitative description of the temperature behavior of dielectric permittivities of the K 1−x (ND 4 )xD 2 PO 4 and Rb 1−x (NH 4 )xH 2 AsO 4 compounds at different frequencies. The origin of low-temperature peak in the imaginary part of dielectric permittivity in proton glasses is discussed.

Section: Discussionmentioning

confidence: 81%

“…The most complete experimental data for Rb 1−x (NH 4 ) x H 2 AsO 4 for the dielectric measurements in a wide frequency range at low temperatures can be found in [23][24][25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics and complex dielectric permittivity of mixed crystals of the Rb_{1-x}(NH_{4})_{x}H_{2}PO_{4} type

Levitsky¹,

Sorokov²,

Stankowski³

et al. 2008

“…: 75.10.Hk, 77.22.Ch, 77.84.F The present paper is a continuation of our recent investigations of ferroelectric-antiferroelectric mixed systems with hydrogen bonds [1][2][3]. There is an abundant experimental material concerning phase diagrams and the behaviour of thermodynamic functions for this mixed crystals [4][5][6][7][8]. The phase diagrams demonstrate the coexistence of pure and mixed ferro-, antiferro-, paraelectric, dipole glass phases in a wide region of temperatures and concentrations.…”

mentioning

confidence: 77%

“…There is an abundant experimental material concerning phase diagrams and the behaviour of thermodynamic functions for this mixed crystals [4][5][6][7][8]. The phase diagrams demonstrate the coexistence of pure and mixed ferro-, antiferro-, paraelectric, dipole glass phases in a wide region of temperatures and concentrations.…”

mentioning

confidence: 99%

Ferroelectric-antiferroelectric mixed systems. Equation of state, thermodynamic functions

Korynevskii¹,

Solovyan²

2006

The problem of equation of state for ferroelectric-antiferroelectric mixed systems in the whole region of a concentration change (0 n 1) is discussed. The main peculiarity of the presented model turns out to be the possibility for the site dipole momentum to be oriented ferroelectrically in z-direction and antiferroelectrically in x-direction. Such a situation takes place in mixed compounds of KDP type. The different phases (ferro-, antiferro-, paraelectric, dipole glass and some combinations of them) have been found and analyzed. : 75.10.Hk, 77.22.Ch, 77.84.F The present paper is a continuation of our recent investigations of ferroelectric-antiferroelectric mixed systems with hydrogen bonds [1][2][3]. There is an abundant experimental material concerning phase diagrams and the behaviour of thermodynamic functions for this mixed crystals [4][5][6][7][8]. The phase diagrams demonstrate the coexistence of pure and mixed ferro-, antiferro-, paraelectric, dipole glass phases in a wide region of temperatures and concentrations. A theoretical description of such systems is in its initial stage so far. The main approach is based on the statistic replica method for calculating the thermodynamic functions for a mixed system with non-equilibrium distribution of differently occupied sites, similar to the ones exploited in mixed ferromagnetic system investigations [9]. Key words: ferroelectrics and antiferroelectrics, mixed systems, equation of state PACSIt is well known that short range interparticle interactions play an important role in ferroelectrics (especially in hydrogen bonded ones). So, in order to adequately describe the ferroelectricantiferroelectric mixed systems we should take into account both the short and long range interactions. An effective method was proposed in [2], where the model Hamiltonian includes two subsystems of particles with dipole momenta perpendicular to each other, with short and long range interaction between them and which depend on the probability of occupying each lattice site. In the second order of replica expansion for −βH (β = (kT ) −1 , k is the Boltzmann constant and T is the absolute temperature) the free energy of the system investigated has been obtained. The equations for ferroelectric P = S z , antiferroelectric ξ = S x order parameters and dipole glass g z = S z mi S z m i , g x = S x mi S x m i parameters were found. Here · · · denotes thermal averaging for a given distribution of z-and x-oriented dipole momenta of particles whereas a bar denotes a stochastic averaging over different distributions; m, m denotes the nearest neighbours of particles in i-th size. The obtained phase diagram (the temperature of the corresponding order parameter appearing versus concentration) shows a possibility of different phases occurring: ferro-, antiferro-, paraelectric, dipole glass and some combinations of them.The purpose of the present paper is to perform a continual study of ferroelectric-antiferroelectric mixed system taking into account the interaction processes between both subsys...

“…The approximation on the basis of experimental data ( [17]) gives the value T 0 ≈30 K for x=0.36. According to the experimental data [18,94] …”

Section: Phase Diagramsmentioning

confidence: 99%

Thermodynamics, dielectric permittivity and phase diagrams of the Rb_{1-x}(NH_{4})_{x}H_{2}PO_{4} type proton glasses

Sorokov¹,

Levitskii²,

Vdovych³

2010

The cluster pseudospin model of proton glasses, which takes into account the energy levels of protons around the PO 4 group, the long-range interactions between the hydrogen bonds, and an internal random deformational field is used to investigate thermodynamical characteristics, longitudinal and transverse dielectric permittivities of Rb 1−x (ND 4 )xD 2 PO 4 and Rb 1−x (NH 4 )xH 2 AsO 4 compounds. A review of experimental and theoretical works on the Rb 1−x (NH 4 )xH 2 PO 4 type crystals is presented.