Competition between the chiral smectic-C* and hexatic phases.
A theory of the phase transition from the smectic-C* to the hexatic phase based on the free energy with the two different Lifshitz terms is presented. Competition between the elastic energies of the tilt angle and of the hexatic order leads either to the single helicoidal structure, or to the double modulated solitonlike structure, and the transformation between both can occur. The bond order and the tilt angle suppress each other and at the transition to the low-temperature hexatic phase a decrease of the tilt angle and an anomaly in the helical pitch occur. Approaching the hexatic phase transition the dielectric response is contributed mainly by the bond-order phason or (and) the tilt angle phason. While the bond-order phason frequency decreases the tilt angle frequency increases in the hexatic phase. Both situations are treated being observed in experiment.