Collective dielectric relaxation in smectic A and smectic C⋆ phases near transition temperature of electroclinic liquid crystals

Abstract

The collective dielectric relaxation processes of electroclinic liquid-crystal materials have been investigated in a thin (3.5μm) planar cell in the frequency range of 1 Hz–10 MHz. Measurement of complex dielectric permittivity versus temperature has been taken on aligned samples filled with different electroclinic liquid-crystal materials. The dielectric data were collected by using the measuring electric field perpendicular to the smectic layer planes. The behavior of the collective dielectric modes has been studied in smectic C*(SmC*) and smectic A(SmA) phases. However, near the transition temperature of SmC*-SmA phase, the dielectric permittivity due to the Goldstone mode and soft mode could not be separated. It has also been observed that the dielectric permittivity increases with temperature before the transition temperature of SmC*-SmA phase under bias field. Temperature dependence of dielectric increments before the transition temperature under bias field and relaxation frequency suggests that the electroclinic liquid crystal shows transitional behavior over a wide temperature range and does not obey the Curie–Weiss law near the transition temperature like in other ferroelectric liquid-crystal materials.