| From X-ray experiments performed on oriented samples of (R-)-chloro-2-propyl-p-hexyloxybenzylidene-p'-aminocinnamate (HOBACPC) by means of an electric field, we have identified two new ordered smectic phases which appear at lower temperature than the ferroelectric Sm C* phase. These two phases are characterized by a pseudo-hexagonal order within the layers, but they differ from the Sm Bc phases by the direction of the long molecular axes which are tilted in a plane parallel to an edge of the pseudo-hexagonal lattice. One of these new phases shows a three-dimensional order, whereas the other one, which appears when increasing the temperature, shows only a two-dimensional order, the smectic layers being almost uncorrelated. This structure is probably connected with the ferroelectric behaviour of this last phase, which is analogous to that exhibited by the Sm C* phase. |
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