X-ray and optical studies of the tilted phases of materials exhibiting antiferroelectric, ferrielectric and ferroelectric mesophases

Abstract

X-Ray and optical techniques have been employed to probe the physical properties of six materials that exhibit various frustrated chiral smectic phases. The temperature dependent evolution of the layer spacing, measured by small angle X-ray diffraction, is discussed with respect to the molecular structures of the materials. The layer spacings are used to deduce the steric tilt angle of the systems across the ferro-, ferri- and antiferro-electric phase ranges. Measurements of the steric and saturated optical tilt of the phases are compared. In general, for most materials and at most temperatures, the steric tilt is lower than the X-ray tilt as would be expected. However, in three of the materials the X-ray tilt is higher than the optical tilt over part of the high temperature tilted phase regime, providing evidence of conformation driven inversion phenomena. Further, the ratio of the steric to optical tilt angle is strongly temperature dependent in all but two of the materials.