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

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