LINEAR ELECTROCLINIC COUPLING IN FERROELECTRIC LIQUID-CRYSTALS

We report a study of the electroclinic coupling (soft mode), close to the smectic A to smectic C* phase transition in several chiral compounds. The main characteristic of the technique used is to measure both optical and dielectric quantities on a single sample. This way one may derive the first coefficients of the Landau expansion describing the phase transition. The simplest expectations of this theory are found to hold well without unusual temperature dependences of the coefficients. Furthermore, the relaxation frequency of the electroclinic coupling, (which is essential for applications), is found to lie in the 10 kHz to 1 MHz range.