MEAN-FIELD COEFFICIENTS AND THE ELECTROCLINIC EFFECT OF A FERROELECTRIC LIQUID-CRYSTAL

Experimental data on the temperature and electric field dependence of the tilt angle and the electroclinic effect of the smectic-C (Sm-C*) and the smectic-A (Sm-A*) phases are presented which have been obtain ed by electrooptical investigations on the ferroelectric liquid crysta l mixture FLC 6430 from Hoffmann-La Roche, Basle, Switzerland. The dat a are analyzed according to the generalized Landau expansion and the r esults of a microscopic model for spontaneous polarization. The mean-f ield coefficients obtained from a fit of the Landau approach to the ex perimental data are discussed with respect to the electroclinic effect , the specific heat singularity, and the chirality. The results suppor t the evidence of quadrupolar ordering and biquadratic coupling for th e description of the Sm-C-Sm-A* phase transition. The Landau model is extended to temperatures far below the phase transition.