Transitions from the SmC* or SmC* A Phases to the Tilted Hexatic Phases Studied by the Dielectric Spectroscopy

At the phase transition from SmC* or SmC* A to the tilted hexatic phase the spontaneous polarization, tilt angle and the length of the helical pitch significantly decrease. Dielectric spectroscopy exhibits a single relaxation process in the vicinity of these transitions, which can be attributed to fluctuations of bond orientational order (BOO) coupled to the tilt and polarization. The anomalies of both the relaxation frequency and the dielectric strength of the mode at the transition as well as behavior of spontaneous quantities are discussed on the basis of a new theory, which takes into account a competition of the space modulation of tilt and BOO order parameters.