MOLECULAR ORIENTATIONAL STRUCTURES IN FERROELECTRIC, FERRIELECTRIC AND ANTIFERROELECTRIC SMECTIC LIQUID-CRYSTAL PHASES AS STUDIED BY CONOSCOPE OBSERVATION

Molecular orientational structures in MHPOBC were studied by means of conoscope observation. Contrary to a ferroelectric response of the conoscope to an electric field in the smectic C*phase, the conoscopic figure in the antiferroelectric smectic CAphase does not shift its center and is biaxial with its optic plane perpendicular to the field direction. This conoscope change is only due to a dielectric contribution, indicating the existence of the inherent threshold in the electric field induced transition to the ferroelectric phase. In between the ferroelectric and antiferroelectric phases, a kind of ferrielectric phase was clearly distinguished in the field response of the conoscopic figure; the shift of the conoscope center perpendicular to the applied field and the biaxial optic plane parallel to the field suggest a novel molecular orientational structure. © 1990 IOP Publishing Ltd.