J. Phys. II France
Volume 5, Number 12, December 1995
Page(s) 1793 - 1803
DOI: 10.1051/jp2:1995208
J. Phys. II France 5 (1995) 1793-1803

Raman Scattering and Defects in Liquid Crystals Exhibiting Ferrielectric Phases

R. Farhi1, M. Sidir1 and H.T. Nguyen2

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

(Received 28 June 1995, accepted in final form 15 September 1995)

Polarized Raman scattering experiments have been performed on tolane series compounds which exhibit a ferroelectric-ferrielectric antiferroelectric phase sequence. Very strong discontinuities in ratios or absolute values of integrated Raman intensities are observed at each transition including those from or to the smectic C $^*_\alpha$ phase when it is present. More particularly, drastic steps are obtained in the vicinity of the ferrielectric phase(s). The data can be understood as a superposition of a regular part related to the tilt angle variation and of drops (or enhancements) of the Raman intensity resulting from second order local field effects induced by charged defects such as disclination lines.

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