Dielectric studies in the vicinity of the A-C* transition

Abstract

We have studied the soft mode and Goldstone mode relaxations in a ferroelectric liquid crystal compound (referred to as C6 for short) exhibiting a high value of spontaneous polarisation. The results show that the relaxation frequency f_s as well as the dielectric strength Δϵ _S can be described by a simple power law, but gives non-mean field exponents. However, fitting done to the Δϵ _s data using an expression given by the generalised mean field theory, not only yields the mean field susceptibility exponent γ but also helps in determining the Landau coefficients a and C (where a is the electroclinic coefficient and C the polarisation-tilt coupling constant) as well as the soft mode viscosity. We also present the Goldstone mode viscosity and the relevant elastic torque data. Measurements on C7 and C8, the higher homologs of C6, bring out the effect of chain length on the relaxation parameters.

Key Words:

• Goldstone mode
• soft mode
• Landau coefficients
• effect of chain length