DEVILS STAIRCASE FORMED BY COMPETING INTERACTIONS STABILIZING THE FERROELECTRIC SMECTIC-C-ASTERISK PHASE AND THE ANTIFERROELECTRIC SMECTIC-C-ASTERISK(A) PHASE IN LIQUID-CRYSTALLINE BINARY-MIXTURES

In order to demonstrate experimentally that the competition between the antiferroelectric and ferroelectric interactions stabilizing SmC(A)* and SmC* (the pairing energy of the transverse dipole moments in adjacent smectic layers and the packing entropy resulting from the excluded volume effect) produces a variety of antiferroelectric and ferrielectric subphases in the temperature region between antiferroelectric SmC(A)* and ferroelectric SmC*, we have tried to observe the subphases in several binary mixtures of chiral smectic liquid crystals. The subphases were identified by the electric field dependence of conoscopic figures and the apparent tilt angle as a function of field strength. Systematically changing the mixing ratio of two properly chosen compounds and studying the stability of each subphase, we have substantiated that the subphases between SmC(A)* and SmC* form a Devil's staircase, SmC(A)*(q(T)). Here, q(T) is an irreducible rational number, which specifies a fraction of the ferroelectric ordering in the antiferroelectric ordering. We have also discussed the relationship of SmC(A)*(q(T)) to the other staircase, SmC(alpha)*(q(T)), that was proposed to exist as a result of the rather macroscopic, electrostatic interaction among two-dimensional spontaneous polarizations in smectic layers.