The antiferroelectric TGB phase: textures, field-induced effects and microscopic model

By studying the optical textures and the field-induced effects of the recently discovered TGBCAphase we have developed a qualitative model of the microscopic organization of the phase. Inside the smectic blocks, the molecular tilt plane of the local anticlinic structure is perpendicular to the helix of the TGBC A phase. The grain boundaries consist of a regular lattice of +1/2 and -1/2 dispirations; i.e. unit screw dislocations combined with half unit disclinations. Whereas all screw dislocations have the same sign, the sign of the half unit disclinations alternates in adjacent dispirations. Hence, in the grain boundaries the molecular tilt plane between adjacent dispirations is alternately parallel and perpendicular to the TGB helix.