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

Abstract

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.

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

“…It should be noted that in [196] based on the unified proton ordering model proposed in this paper and in the cluster approximation, we calculated the physical characteristics of the Rb 1−y (NH 4 ) y H 2 PO 4 type systems. A satisfactory quantitative description of experimental data was obtained.…”

“…Their thermodynamic and dynamic characteristics were calculated using simple models of the KH 2 PO 4 family ferroelectrics (see [196]). Only in [193][194][195] the cluster approach was used in describing the experimentally observed phase diagrams of the Rb 1−x (NH 4 ) x H 2 PO 4 type systems.…”

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

“…In [82,83] a similar approach has been used for the description of some thermodynamic characteristics and transverse dielectric permittivity of hydrogen bonded Rb 1−x (ND 4 ) x D 2 PO 4 and Rb 1−x (NH 4 ) x H 2 AsO 4 compounds, in which an essential role in the formation of energy levels is played by the proton short-range correlations. The goal of the present paper is to calculate the thermodynamic characteristics, the longitudinal and transverse dielectric permittivities of these compounds at different temperatures, concentrations, and frequencies, as well as to determine their phase diagrams.…”

“…The temperature dependence of transverse permittivity for the Rb 1−x (ND 4 ) x D 2 PO 4 and Rb 1−x (NH 4 ) x H 2 AsO 4 compounds was explored in previous papers [82,83].…”

Диэлектрические, электромеханические и упругие свойства монокристаллов Rb-=SUB=-1-x-=/SUB=-(NH-=SUB=-4-=/SUB=-)-=SUB=-x-=/SUB=-H-=SUB=-2-=/SUB=-PO-=SUB=-4-=/SUB=-

“…Позже была развита кластерная теория для описания тер-модинамических и динамических свойств систем типа Rb 1−x (NH 4 ) x H 2 PO 4 [5][6][7][8][9], которая при надлежащем вы-боре параметров позволила удовлетворительно описать диэлектрические и поляризационные свойства этих ма-териалов без учета пьезоэлектрической связи. Вместе с тем необходимость такого учета следует из анализа ряда работ.…”