Smectic-C*alpha phase with two coexistent helical pitch values and a first-order smectic-C*alpha to smectic-C* transition.

Previous results from Kundu using dielectric relaxation have suggested a reentrant antiferroelectric-ferroelectric-antiferroelectric transition in the compound LN36. Our comprehensive studies of this compound using differential optical reflectivity, nonadiabatic scanning calorimetry, null transmission ellipsometry, and resonant x-ray diffraction show that in fact LN36 exhibits the usual phase sequence for chiral smectic liquid crystals: SmA*-SmCalpha-SmC-SmCFI1-SmCA . Moreover, the SmCalpha-SmC transition is a first-order transition, characterized by a discontinuous change in the helical pitch. At temperatures just above the SmCalpha-SmC transition, two different values for the helical pitch are simultaneously observed for the first time.