RAMAN-SCATTERING AND DEFECTS IN LIQUID-CRYSTALS EXHIBITING FERRIELECTRIC PHASES

Polarized Raman scattering experiments have been performed on tolane s eries compounds which exhibit a ferroelectric-ferrielectric-antiferroe lectric phase-sequence. Very strong discontinuities in ratios or absol ute values of integrated Raman intensities are observed at each transi tion 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 superp osition of a regular part related to the tilt angle variation and of d rops (or enhancements) of the Raman intensity resulting from second or der local field effects induced by charged defects such as disclinatio n lines.