LANDAU EXPANSION COEFFICIENTS FOR A FERROELECTRIC LIQUID-CRYSTAL SHOWING A POLARIZATION SIGN INVERSION

Capacitance, pyroelectric and electrooptical measurements have been ca rried out over a certain temperature range near the smectic A-C phase transition for a Chisso compound showing the sign inversion of the sp antaneous polarization with temperature. Two Landau expansion coeffici ents, namely, the polarization-to-tilt coupling constant C and the til t elastic coefficient cc have been calculated. Coefficient a is close to that known for conventional ferroelectric liquid crystals (e.g., DO BAMBC), coefficient C manifests nonmonotonic temperature dependence wi th a maximum well above the A-C transition and an inflection point at the transition. This behaviour may qualitatively be understood if the biaxiality induced by a molecular tilt is taken into account.