Electric Field Induced Texture Transitions in the Planar Smectic A Phase of Some Cyanobiphenyls

Observations of zero field textures and electric field induced defects in the planar smectic A of the cyanobiphenyl group of liquid crystals are presented. Two transitions, first from the parabolic focal conic texture to a texture consisting of array line defects and then to a quasi-homeotropic texture are observed under the influence of an electric field. The line defects are interpreted as edge dislocations. The current-voltage characteristics and the electro-optic studies confirm the existence of the above two transitions. A long optical memory effect is realised from the electro-optic studies. A decrease in the current density is associated with the transition to the memory state.