Textures and structure of the low temperature liquid crystal phases of HOBACPC [(R-) hexyloxybenzylidene p'-amino-2-chloropropyl cinnamate]

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Abstract
HOBACPC is known to exhibit three helielectric phases identified as C*, I* and (G')* or J*. Here we present evidence that a truly ferroelectric phase, X, exists at lower temperatures than these phases. Owing to their helicoidal structure, the spontaneous polarization of helielectric phases globally averages to zero. In bulk samples they are not usually bistable (by bistable we mean that the field induced configuration remains when the field is removed) so that when the field E is turned off, the helicoidal structure returns. In contrast, long range inter-layer correlations suppress the helicoidal structure in smectic X and it is bistable. We argue that the cross-over from helielectric to ferroelectric behaviour takes place in the (G')* phase since it is characterized by finite inter-layer correlations resulting in a non-uniform helicoidal structure. Because many tilted smectic phases have been discovered recently and there have been numerous changes in nomenclature, we find it useful to review our current understanding of the structural features of these phases as they may apply to HOBACPC in an appendix