J. Phys. II France
Volume 7, Number 12, December 1997
Page(s) 1817 - 1828
DOI: 10.1051/jp2:1997216
J. Phys. II France 7 (1997) 1817-1828

Optical Properties and Phenomenological Theory of Ferri-Ferri Phase Transitions in Antiferroelectric Liquid Crystals

P. Gisse1, M. Sidir1, V.L. Lorman1, R. Farhi1, J. Pavel1 and H.T. Nguyen2

1  Laboratoire de Physique de la Matière Condensée, Université de Picardie Jules-Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France
2  Centre de Recherche Paul Pascal, avenue A. Schweitzer, 33600 Pessac, France

(Received 20 January 1997, revised 16 July 1997, accepted 2 September 1997)

Optical rotatory power and Raman scattering experiments on chiral liquid crystals belonging to a series which exhibits one or two ferrielectric phases have been performed. The results of these non-perturbative techniques show that, depending upon the aliphatic chain length, a first order transition with a jump in sign and value of the helical pitch, or a divergence and sign reversal of the pitch with no transition can occur in these systems. These observations are in agreement with a generalized Landau-de Gennes phenomenological model predicting that the ferrielectric phases, when both exist, should be isostructural.

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