Condensed Matter Physics, 1996, No. 7, p. 163-177, English
DOI:10.5488/CMP.7.163
Title: THE ANALYSIS OF FERROELECTRIC TYPE INSTABILITIES IN THE
TWO-SUBLATTICE MODEL OF HIGH TEMPERATURE SUPERCONDUCTING SYSTEMS
Authors: O.D.Danyliv, I.V.Stasyuk (Institute for Condensed Matter Physics
Ukrainian National Academy of Sciences, 1 Svientsitskii St.,
290011 Lviv-11, Ukraine)
The two-sublattice pseudospin model of Mitsui type
supplemented by the interaction with electron subsystem is considered.
Such a model can be used for the
description of dielectric properties of YBaCuO-type superconductors
along c-axis (the pseudospins represent anharmonic motions of
apical oxygen O4). The behaviour of the
the transverse dielectric susceptibility \chi_\perp is considered in the
noninteracting clusters approximation.
Possibility of different temperature dependencies of \chi_\perp is established.
The free energy of the model is evaluated in the mean field
approximation. It is established that the long-range interaction
between pseudospins can lead to symmetry breaking
and to appearance of the ferroelectric component of pseudospin ordering.
The phase transitions into the state with decompensated dipole moments can
be both of second and first order. The corresponding (Tc, h) diagrams
(h is the asymmetry parameter of the field acting on pseudospins) at
different values of long-range interaction constants in the regimes of
fixed values of electron concentration (n=const) or chemical potential
(\mu=const) are obtained. The anomalies of susceptibility \chi_\perp
in the vicinity of phase transitions points are investigated.
Comments: Refs. 11, Figs. 8, Tabs. 0.