Relaxation precesses in the ferroelectric and alpha phases of antiferroelectric liquid crystals

Dielectric measurements of a new antiferroelectric liquid crystal series exhibiting different phase sequences have been carried out as a function of frequency from 10 Hz to 10 MHz. Structural properties of S-C alpha* and ferrielectric S-CFI* phases were discussed on the basis of the experimental results of temperature and de bias field dependencies of the dielectric modes. Besides the soft mode observed around the S-A - S-C alpha* phase transition: a Goldstone mode was detected in the S-C alpha* phase indicating a helicoidal structure with small Ditch values. in agreement with a bilayer ordering model, the dielectric absorption in the S-CFI* phase was splitted up into two contributions: one related to a Goldstone mode and the other to an azimuthal antiphase mode.