Phase Diagram of a Ferroelectric Chiral Smectic Liquid Crystal near the Lifshitz Point

The phase diagram of chiral smectic $p$-decyloxybenzilidene-$p^{\prime }$-amino-2-methylbutyl cinnamate in an external magnetic field parallel to the smectic layers has been determined by dielectric and optical measurements up to 14.5 T. The data indicate the existence of a Lifshitz point between the disordered smectic-$A$, the modulated smectic-$C^{*}$, and the homogeneously ordered smectic-$C$ phases. A reentrant $C^{*}$ phase has been found above 8.5 T. The critical field for the unwinding of the helix becomes extremely large as the $\lambda$ line is approached.