Low Frequency Dielectric Relaxation, Spontaneous Polarization, Optical Tilt Angle and Response Time Investigations in a Flourinated Ferroelectric Liquid Crystal, N125F2(R*)

Abstract

Experimental investigations of thermal microscopy, low frequency dielectric relaxation, spontaneous polarization P _s (T), optical tilt angle θ(T) and response times τ _s (T) are carried out in a fluorinated ferroelectric liquid crystal, N125F2(R*) exhibiting smectic-A and smectic-C* phases. Dielectric loss in the smectic-A phase exhibits single Debye's relaxation in the MHz region. The smectic-C* phase exhibits two relaxations, viz., a Goldstone mode at ∼500 Hz and another at a much higher frequency, ∼5 MHz. The Arrhenius shift of Smectic-A relaxation frequency (f _R ) gives an activation energy of 1.5 eV. The influence of temperature and applied voltage on the smectic-C* Goldstone mode relaxation is studied. In the smectic-C* high frequency relaxation mode, the relaxation frequency (relevant to the tilt) is found to increase with decreasing temperature. The temperature variation of the reciprocal of the dielectric strength (1/Δϵ _s ) above the smectic-A—smectic-C* phase transition qualitatively supports the Curie-Weiss law. Temperature variation of primary (tilt) and secondary (P _s ) order parameters are presented. The temperature variation of τ _s in the smectic-C* phase studied through square wave technique is presented. The influence of fluorine atoms on the rigid core part of the present ferroelectric liquid crystal on the physical properties exhibited in it's smectic-C* phase is discussed.

Keywords:

• Ferroelectric liquid crystals
• dielectric relaxation
• Goldstone and soft modes

Acknowledgements

This work was supported by the project IG/SCI/PHYS/00/02 financed by Sultan Qaboos University. One of the authors, DMP is grateful to Sultan Qaboos University for the Visiting Consultant position.