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The layer structure in the antiferroelectric, ferrielectric, and ferroelectric phases of a liquid crystal device is reported, together with its electric field-induced deformation. The field-free chevron angle is comparable to the steric tilt angle, but differs significantly from the optical tilt angle. A sharp field threshold is observed for the chevron to bookshelf transition in the antiferroelectric phase at 1.3 V/mm, while layer deformations occur at much lower fields ~0.3 V/mm! in the other subphases. Models are proposed for the layer deformations. © 2000 American Institute of Physics. @S0003-6951~00!00129-7# Ferroelectric liquid crystals are formed from rodlike chi- ral molecules, arranged in layers with their average molecu- lar direction ~director! tilted with respect to the layer normal by a temperature-dependent angle.1 Within a device the di- rector defines the optic axis and is readily switched to posi- tions on either side of a symmetry axis by an electric field, providing an electro-optic switch. The tilt angle increases with decreasing temperature and the resulting change in layer spacing usually induces a chevron structure in a device,2 which is transformed to a bookshelf geometry on application of a sufficiently high electric field 3,4 ~Fig. 1!. The complex director configurations that can be accommodated by the chevron structure influence device electro-optic prop- erties, so it is important to study both the chevron structure and its field-induced changes in liquid crystal devices. This can be done effectively by x-ray diffraction. Such studies are also relevant to antiferroelectric and ferrielectric liquid crys- tals, though there are few reports of the temperature dependence5 or field response 6,7 of the chevron structure in the antiferroelectric phase, and none in ferrielectric phases. This paper presents the temperature dependence of the chev- ron structure in a material exhibiting ferro-, ferri-, and anti- ferroelectric phases, together with the evolution of the field- induced layer deformations in each of the chiral subphases. The measurements are discussed in context with electro- optic studies of the same device. The material used, denoted AS573, was synthesized at Hull University, UK and has been studied extensively.8-10

Electric field-induced layer deformations in the subphases of an antiferroelectric liquid crystal device