Defects in ferroelectric and antiferroelectric liquid crystals

In ferroelectric (FE) and antiferroelectric (AF) phases of chiral smectic C (S-C*) liquid crystals typical line defects like dislocations and disclina tions exist. In this review a few examples of these defects will be mention ed: In thick samples the anchoring conditions impose the presence of two system s of (2 pi)-twist disclinations (called also,"unwinding lines") near both g lass plates. In S-C* samples with the chevron layer structure the chevron plane is actin g as a barrier to the propagation of the director deformation. Overcoming t his barrier leads to the creation of so called "inversion line" which is pi -twist disclination in the chevron plane, In thicker free-standing FE or AF films the observed stripe texture was int erpreted as a periodic system of director discontinuity walls starting on b oth free film surfaces and terminated in the volume of the film. Line defects called dispirations which are combinations of layer dislocatio ns and director disclinations were observed in AF phases.