Onset and evolution of the tilted smectic antiphase in a polar liquid-crystal binary mixture

High-resolution x-ray diffraction studies of a binary mixture of the n=8 and n=10 homologs of alkoxyphenyl nitrobenzoyloxy benzoate DBₙ{ONO}₂$ (52.6 mole % ${DB}₁₀ONO₂) have been performed at the onset of the tilted smectic antiphase (Sm-C ̃ \~{}{}) upon cooling from the smectic-A₁ phase. Fluctuations of the two competing smectic orders are found to be related to monolayer and partial bilayer ordering. With decreasing temperature, the period of the antiphase in-plane modulation increases while the smectic layer normal tilts at an angle of ±{}7^∘{} with respect to the director. This tilt partially recovers upon the transition to the smectic-A₂ phase. {} 1996 The American Physical Society.