A temperature-concentration (T-X) phase diagram calculated using the mean field theory for liquid crystals.

Phase-line equations for smectic-hexatic phase transitions in liquid crystals were derived using the Landau phenomenological theory. In particular, second-order transitions for the smectic-A-smectic-C (SmA-SmC) and hexatic-B-hexatic-F (or HexI) transitions were studied and the tricritical points for these transitions were located. The calculated phase-line equations were fitted (using experimental data for various liquid crystals) to construct a generalized T-X phase diagram. It was shown that the T-X phase diagram calculated from the free energy adequately describes the observed behavior of liquid crystals during smectic-hexatic transitions.