Behaviour of the Soft Mode in the Smectic A* and C* Phases Studied By Dielectric Measurements

The temperature and frequency dependence of the soft mode contribution to the dielectric constant of a ferroelectric liquid crystalline system have been studied experimentally. By applying a bias electric field in the C* phase, strong enough to unwind the helix, we have been able to study the soft mode comparatively deep into the C* phase. From the experimental data we have determined the dielectric strength and the relaxation frequency as a function of temperature. In the A* phase and in the C* phase the relaxation frequency and the inverse of the dielectric strength of the soft mode vary linearly with |T-TC|. This experiment also offers a way to determine the C*—A* phase transition temperature to a good accuracy.