Dielectric relaxation in the smectic-A/emph> and smectic-C/emph> phases of a ferroelectric liquid crystal

Abstract

The results of a study of the dielectric properties of a room-temperature ferroelectric liquid crystal in the frequency range from 5 Hz to 13 MHz are presented here. Measurements of complex electric permittivity versus temperature have been taken on aligned samples of different thicknesses with the electric measuring field being parallel or perpendicular to the layer planes. In homogeneously aligned samples two dielectric relaxation regions have been observed in the smectic-$C^{\mathrm{*}}$ phase, one known as the Goldstone mode and the other showing up in the vicinity of the smectic-$C^{\mathrm{*}}$–smectic-$A^{\mathrm{*}}$ transition called the soft mode. In homeotropically aligned samples the low-frequency molecular relaxation was observed in both smectic phases. Temperature dependences of both dielectric increments and relaxation times suggest that the system studied exhibits a ferroelectric phase transition of the first-order type.