DIRECT MEASUREMENTS BY THE PULSE PYROELECTRIC TECHNIQUE OF THE SOFT-MODE RELAXATION-TIMES ON BOTH SIDES OF THE SMECTIC A-C-ASTERISK TRANSITION

The submicrosecond pulse pyroelectric technique has been applied to th e measurements of the soft mode relaxation times on both sides of the ferroelectric smectic A - C phase transition for two ferroelectric li quid crystals, a room temperature multicomponent mixture with high spo ntaneous polarisation; and a compound with polarisation changing its s ign at a certain temperature. Inverse relaxation times seem to obey Cu rie-type behaviour, at least on the smectic A side of the transition. ''Tilt-viscosity'' coefficient gamma theta has been calculated for bot h the materials.