Dynamics of Ferroelectric Rochelle Salt

Abstract

Phys. Rev. 168, 43 (1968)j report a calculation for Fe ' which is qualitatively similar to the present system. Although the KP method was used, a subsequent calculation by D. Ikenberry (private communication) using the MP Dalgarno method gave almost exact agreement, shell by shell, with the EP calculation. The estimates of the corrections discussed for the EP method should therefore apply to the present MP calcul. ation.A quantum theory of ferroelectricity in Rochelle salt is developed which is an extension of the two-sublattice model of Mitsui. The isotope effects on deuteration are explained in a natural way, and the spontaneous polarization, the polarization of the two sublattices, and the dielectric constant are obtained as functions of temperature.The dynamics of the system is investigated for the case of deuterated Rochelle salt and is found to exhibit a twomode relaxational behavior. The correlation time of one of these two modes is proportional to the static dielectric constant and thus exhibits a critical slowing-down on approaching the two Curie temperatures in agreement with the experimental data.

Peculiarities of Neutron Scattering by Order-Disorder Antiferroelectrics

“…It was supplemented by Müller's (electron-pseudospin) "field" [H z i = g l n i+l -representing the role of electron carrier density n i+l of four oxygens (index l) in CuO 2 sheet near the i-th O4] as well as by the coupling of the O4-tunnelling motion with Cu 2 -O 2 ,O 3 -vibrations (modes) of A g -or B g -symmetry (analogous to E qj+ modes) [19,21,33]. Unlike the present neutron scattering analysis, it is tempting to conclude that the well-enough refined cross sections [equations (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)] could be applied to dismiss many controversies in testing the existence of structural, dielectric and charge instabilities, asymmetry of the local Cu 2 −O4−Cu 2 potential, vibronic states, etc., up to the problem of the mutual origin of superconducting and (anti)ferroelectric phases, i.e. their possible coexistence.…”

“…The relevant numerical calculations of mean values S z 1 and S z 2 including two relaxation times, τ q± , corresponding to two (degenerated) modes ω q± = ω q , ω q+q B (equation (13)) for deutered RS have been done whereby a good agreement with experimental data has been obtained [18] (cf. [2]).…”

“…Tentatively such dipoles could be coupled with heavy ions of distorted octahedra of tartrate groups (C 2 O 6 ) in common with Na-and K-ions. Based on more reliable structural data and on refined experimental studies, neutron scattering intensities should be fitted by the expressions presented, using very successful numerical estimations as given in [15,18]. In such a way, the controversy about the nature (i.e.…”

“…Such compounds are typified by ADP-crystal as entirely KDP-type antiferroelectric, and we shall deal with them predominantly throughout this paper. The treatment will be extended to another representative hydrogenbonded antiferroelectric, to Rochelle salt, as characterized by an asymmetric doublewell single-particle potential and rather resembling the features of a ferroelectric compound [2,18].…”

Phase transitions in the Mitsui model

“…In 1971, Žekš, Shukla, and Blinc [2] formulated this model in terms of pseudospins and just in this form it is known at the present time.…”