BEHAVIOR OF THE GOLDSTONE MODE IN SMECTIC-C-ASTERISK PHASE AND THE SOFT MODE IN THE SMECTIC-C-ASTERISK AND SMECTIC-A-ASTERISK PHASES OF A FERROELECTRIC LIQUID-CRYSTAL MIXTURE

The complex dielectric permittivity has been measured as a function of temperature, and the bias electric field for a ferroelectric liquid-c rystal mixture having low spontaneous polarization. By applying the I, ias electric field we have been able to measure the soft mode 2 degree s C inside the smectic-C phase. From the experimental results, relaxa tion frequency and dielectric strength of the Goldstone mode in the Sm -C phase and soft mode in the smectic-C* and smectic-A* phases have b een determined. The parameter beta, which determines the importance of biquadratic coupling compared to the bilinear coupling of extended La ndau model near to the transition temperature in the Sm-C phase, has been determined from known valuer of spontaneous polarization and tilt angles at various temperatures. The experimental results have been co mpared to those of numerically calculated values and a good agreement between the results has been obtained. The Sm-C-Sm-A* transition temp erature T-C has been determined from the dielectric results. The devia tion between the T-C determined experimentally and the T-C observed fr om texture studies is around 0.3 degrees C for the ferroelectric liqui d-crystal mixture studied in this paper.