Proton Ordering Model of Phase Transitions in Hydrogen Bonded Ferrielectric Type Systems: The Gpi Crystal

Abstract

A microscopic model based on the consideration of the proton ordering is proposed for describing the H-bonded ferroelectric crystalline systems with a complex structure of the hydrogen bond network. The model has been used for the investigation of thermodynamics and dielectric properties of the GPI crystal. The symmetry analysis of the order parameters responsible for the mixed (ferro-and antiferroelectric) nature of ordering is performed within the model. The phase transition into the ferroelectric state is described. Changes in the dielectric susceptibility of the crystal are studied in the presence of the transverse external electric field acting along the caxis. The results of measurements of temperature and field dependences of dielectric permittivity ε c in the paraelectric phase are presented. The microscopic mechanism of the observed effects is discussed based on the comparison of theoretical results and experimental data. A conclusion is made about the significant role of the ionic groups connected by hydrogen bonds in the charge transfer. So they make an important contribution into the polarizability of the GPI crystal along the direction of H-bonded chains.

Influence of electric fields on dielectric properties of GPI ferroelectric

“…The results of an experimental investigation of the static dielectric permittivity ε 33 of GPI crystal at different values of the field E 3 are presented in [10,11]. The phase transition temperature for this case was 222 K, but the field dependence of the T c is similar to the crystal with T c = 225 K. Therefore, having made the above mentioned changes of the model parameters, we consider it possible to explain the experimental data.…”

Deformation effects in glycinium phosphite ferroelectric

“…The experiment, carried out in [34], revealed anomalies of permittivity ε zz in the phase transition region at E z 0 and a decrease of the phase transition temperature proportional to E 2 z . For the first time, the explanation of the revealed effects was given on the basis of phenomenologic theory [35] and within microscopic approach [34,36]. Unfortunately, a complete quantitative description of these experimental data was not obtained.…”

Dynamic properties of NH_3CH_2COOH·H_2PO_3 ferroelectric

“…, 4; σ q f 2 are pseudospin variables that describe the changes connected with reorientation of the dipole moments. The Hamiltonian of a proton subsystem of GPI, which takes into account the short-range and longrange interactions and the applied electric fields E 1 , E 2 , E 3 along the positive directions of the Cartesian axes X, Y and Z (X ⊥ (b, c), Y b, Z c) can be written in such a way: 1) where N is the total number of primitive cells. The first term in (2.1) is the "seed" energy, which relates to the heavy ion sublattice and does not explicitly depend on the configuration of the proton subsystem.…”

“…In [1][2][3] basing on the analysis of structural data [4] it was determined that the main role in the phase transition in GPI is played by two structurally nonequivalent types of O-H. . .O hydrogen bonds of different length, which connect phosphite groups HPO 3 in the chains along the crystallographic c-axis.…”

“….O hydrogen bonds of different length, which connect phosphite groups HPO 3 in the chains along the crystallographic c-axis. As a result, in [1,3] there was proposed a model of GPI crystal with proton ordering, within which the main peculiarities of its dielectric permittivity were explained qualitatively. Later, this model was supplement by taking into account the piezoelectric coupling of proton and lattice subsystems [5], which made it possible to calculate thermal, piezoelectric and elastic characteristics of GPI.…”