Dielectric and switching parameters of para-, ferro- and antiferroelectric phases of (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(6-perfluorooctanoyloxyhex-1-oxy) biphenyl-4-carboxylate

Abstract

Dielectric and electro-optical response of the title compound (abbreviated as (S) 7F6Bi) have been investigated. The dielectric studies have been carried out in the frequency range of 1 Hz to 35 MHz under planar anchoring conditions of the molecules. Material exhibits paraelectric SmA*, ferroelectric SmC* and a wide temperature range (∼83°C) antiferroelectric phases. The SmA* phase shows soft mode relaxation due to tiltfluctuation of molecules in the MHz region. Its relaxation frequencies decrease with decrease in the temperature. Dielectric strength increases (∼0.2–3.4) with decrease in temperature 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 phase presumably due to antiferroelectric ordering of the molecules. Its dielectric strength varies from ∼0.55 at 104.3°C to 2.20 at 37.6°C. Switching parameters, namely spontaneous polarisation, switching time and rotational viscosity, have also been determined.

Keywords:

• antiferroelectric liquid crystal
• dielectric permittivity and loss
• dielectric relaxation
• soft and Goldstone mode
• spontaneous polarisation
• switching time

Acknowledgement

The authors thank Department of Atomic Energy, Board of Research in Nuclear Sciences (DAE-BRNS) for financial assistance under a research grant no. 2010/34/38/BRNS2038. Avneesh Mishra thanks DAE-BRNS especially for a Junior Research Fellowship under the project.