Higher smectic-layer order parameters in liquid crystals determined by x-ray diffraction and the effect of antiferroelectricity

By observing the higher-order Bragg peaks corresponding to the layer spacing, the smectic-layer order parameters up to the third order were obtained and the center-of-mass distribution function along the layer normal was calculated. The results clearly indicate that the smectic layer distribution is different from a sinusoidal density wave in antiferroelectric liquid crystals and that the smectic- (Sm) layer order is relatively higher in antiferroelectric Sm-CA(*) than in ferroelectric Sm-C(*). There exists a correlation between the stable antiferroelectricity and the higher smectic-layer order.