Pyroelectric properties of ferroelectric liquid crystal cells with chevron, bookshelf, and helical structures

The pyroelectric properties of ferroelectric liquid crystal (FLC) cells possessing helical and surface stabilized structures have been investigated. Pyroelectric properties of a FLC cell depend on the applied voltage, the internal smectic layer structure, and the ratio of the cell thickness to the material pitch d/p0. For surface-stabilized FLC (SSFLC) cells, hysteresis of the pyroelectric signal was observed for both the chevron and the bookshelf structures and is explained by the intermediate domain states that arise from a distribution in the pretilt azimuthal angle. For the chevron structure a reverse hysteresis loop is observed which is explained by a stronger competitive effect of the ionic field compared to the surface anchoring forces. Cells containing helical structures are studied and for cells with a large d/p0 ratio a linear response of the signal to applied voltage is found. Possible implications of the results obtained for SSFLC cells for which the change in the spontaneous polarization in the decreasing voltage cycle occurs for a voltage lower than obtained during a voltage increasing cycle are discussed.