Dielectric behavior of ferroelectric liquid crystals in the vicinity of the transition into the hexatic phase

Collective molecular dynamics was studied in ferroelectric smectic C* and hexatic smectic I* phases by the dielectric method. In the frequency range 1 Hz to 10 MHz one relaxation process was observed in both phases. In the SmC* phase the relaxation frequency of this process linearly decreases and its dielectric strength increases when approaching the SmC*–SmI* phase transition temperature TI. In the SmI* phase the relaxation frequency is one order of magnitude lower and further slightly decreases on cooling. A phenomenological theory has been developed which describes static and dynamic dielectric properties near TI and satisfactorily explains the experimental results. The observed relaxation has been attributed to fluctuations of the bond orientational order coupled to the molecular tilt. A parameter describing the softening of this mode is determined by fitting theoretical results to the experimental data. The model also describes an observed anomalous increase in the spontaneous polarization as a resul...

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