Structure of the liquid-crystal ferrielectric phases as determined by ellipsometry

The unit cell structures of two ferrielectric liquid-crystal phases are det ermined from ellipsometric studies of freestanding films in a nondistorting rotatable electric field. A highly biaxial mode with out-of-plane distorti ons describes all of the data from two different compounds. Qualitative and quantitative features of the data rule our alternate models. We also prese nt a detailed explanation for apparent inconsistencies between previous res onant x-ray and optical experiments.