Dielectric Spectroscopy of an Anti-Ferroelectric Liquid Crystalline Material with Para- and Ferro-Electric Phases

Abstract

The dielectric studies have been carried out in the frequency range of 1 Hz to 35 MHz under planar anchoring conditions of the
studied material (S)-(+)-4-(1-ethylheptyloxycarbonyl) phenyl 4'-(6- perfluorooctanoyloxy hex-1-oxy) biphenyl-4-carboxylate exhibiting
paraelectric , * SmA ferroelectric * SmC and a wide temperature range (∼83°C) anti-ferroelectric * SmCa phases. The soft mode relaxation due to tilt-fluctuation of molecules is observed in MHz region for the * SmA phase. The relaxation frequencies decreases and dielectric strength increases (∼0.2–3.4) with decrease in the temperature for observed soft mode relaxation and follows Curie–Weiss law. The * SmC phase shows Goldstone mode relaxation due to phase fluctuation of molecules with relaxation frequency ∼10 kHz. Only one mode of relaxation has been observed in the * SmCa phase presumably due to anti-ferroelectric ordering of the molecules. Its dielectric strength varies from ∼0.55 at 104.3 °C to 2.20 at 37.6 °C.