Dielectric and esr behaviour of the first mesogenic iron complex: Local ordering of dipole moments in the mesophase

Abstract

The dielectric and ESR behaviour of the smectic liquid-crystal of iron (III) Schiff base (L) complex FeClL₂ was investigated. A variation of the real part of the dielectric permittivity typical for a smeared ferroelectric phase transition was observed in the temperature region of a S _A - S _x phase transition. Anomalies of dielectric behaviour were caused by local ordering of Fe-Cl dipole moments along the chains in smectic layers. The activation energy E=0.09 eV of the low-frequency relaxation mode, determined from time-domain dielectric spectroscopy data, coincides with the activation energy of the process defining the ESR line broadening. The observed relaxation is probably connected with the chlorine intra Fe—Cl…Fe bond jumps (between two sites in the double-minimum potential), which are correlated along the chains.