The temperature dependence of the layer spacings and the average intermolecular distances were studied in smectic A, C, B and nematic phases by X-ray diffraction on non-oriented samples. Two representatives of 4-n-alkoxyphenyl 4’-n-alkoxy benzoates, furthermore their eutectic binary mixture, and ternary ferroelectric mixtures obtained by the chiral additive of (R)-(1-methylheptyl)-1,1’-4’-1 "-terphyenyl-1,4 "-dicarboxilate used in different concentrations were investigated by small and large angle measurements as well.