The existence and nature of One Smectic-A-Hexatic-B-Smectic- I Point.

The binary mixture phase diagram of n-propyl- and n-butyl- 4'-n-decyloxybiphenyl-4-carbpxylate (3(10)OBC and 4(10)OBC) has been investigated by optical microscopy, x-ray diffraction and heat-capacity studies. Here 3(10)OBC and 4(10)OBC have the isotropic (I)-smectic-A (SmA)-hexatic-B and I-SmA-smectic- I (SmI) transition sequence, respectively. This binary mixture study reveals two new features, namely, the existence of the hexatic-B-SmI transition and a SmA-hexatic-B-SmI point where the relevant three phases coexist.