AN ANNNXY MODEL FOR TRANSVERSELY POLARIZED NONCHIRAL SMECTIC LIQUID-CRYSTALS

We propose an axial next nearest neighbour xy (ANNNXY) model to descri be phase transitions in smectic liquid crystals made of bent non-chira l molecules which exhibit transverse polarisation. The model includes a polar and a quadrupolar NN coupling as well as a competing antiferro electric NNN coupling between the layers. As the temperature is lowere d, the most general sequence of phases predicted by the model is: para electric-helielectric (H-af)-antiferroelectric-reentrant H-af-4 layer antiphase-helielectric (H-f)-ferroelectric. We believe that H-f and th e antiphase have been seen in very recent experiments.