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X-ray investigations of a nematic compound exhibits smectic B phase

S.Mohyeddine, R.Somashekar, D.Revannasiddaiah

Wide angle X-ray patterns were recorded at different temperatures in the nematic and smectic-B phases of 4-hexyl-4-[2-(4-isothiocyanatophenyl) ethyl]-1,1-biphenyl. Layer thickness, inter planer spacing and hence the thermal expansion coefficient were determined in smectic-B phase at various temperatures. The orientational distribution function f() has been calculated fromthe angular distribution of the X-ray intensities. The orientational order parameterP2has been determined from f(). Further, following Line ProfileAnalysis (LPA), it is examined theX-ray profiles of outer and inner rings to compute the crystallite size and intrinsic strain present in the sample. It has been observed that the crystallite area in the smectic-B phase is larger than that of crystalline phase, which essentially indicates a reordering of molecules with a stronger inter/ intra molecular interaction in smectic-B phase. In addition, it is also observed that nano-crystallite area in SmB phase decreases with increase in temperature.