Polar smectic liquid crystals exhibit a variety of phases with multilayer ordering. Recent progress in experimental technique and discovery of several ferrielectric and antiferroelectric phases has put forward a number of fundamental problems: whether the known set of structures is exhaustive or other polar smectic phases exist? Is there an interconnection between azimuthal ordering of molecules in smectic layers and other degrees of freedom such as polar orientation of molecules? We employed the discrete Landau model of phase transitions with two-component order parameter to calculate the structures and phase diagrams of polar smectic liquid crystals. Structures commensurate and incommensurate with layer spacing are formed due to frustrating next-nearest interlayer interaction. Sequences of phases on temperature and the dependence of the phase sequences on model parameters are studied. Influence of different interlayer interactions on the topology of the phase diagrams is analyzed. The calculated phase diagrams enable to describe formation of various polar phases and their temperature sequences, including the unusual reversed phase sequence and the polar phase with six-layer periodicity. Our calculations also predict the existence of a reentrant phase sequence with two incommensurate phases. The results of our calculations demonstrate that discrete Landau model of phase transitions can be successfully used to describe the manifold of polar smectic structures observed in experiment.
Co-authors: P.V.Dolganov (Institute of Solid State Physics, Chernogolvka, Russia), V.M.Zhilin (nstitute of Solid State Physics, Chernogolvka, Russia), V.K.Dolganov (nstitute of Solid State Physics, Chernogolvka, Russia)