Ferrielectric smectic phases: Liquid crystal structure and macroscopic fluctuations

The work concerns the structures and properties of multilayer smectic phases with complex tilt and dipolar order. The symmetry and thermodynamical classification of multilayer antiferroelectric and ferrielectric phases is given. The main attention is paid to the difference of these phases with respect to classical ferroelectric S-c*. A two-layer model of the ferrielectric smectic phase is generalized to describe the sequence of the first order phase transitions ferro-ferri-antiferro-electric and to show the possibility of existence of two isostructural ferrielectric phases, which differ in the value of the helical pitch and in the sense of the helix.