Tricritical behavior of the smectic-A to hexatic-B phase transition in a liquid crystal mixture

A phenomenological approach to the description of the smectic-A-hexatic-B-crystal-B phase sequence in a liquid crystal mixture is proposed. The problem of the first or second-order nature of the smectic-A-hexatic-B transition is explored by means of the variation in the concentration. The influence of the concentration on the smectic-A-hexatic-B-crystal-B phase sequence is discussed by varying the coupling between crystalline order parameter, hexatic order parameter and the concentration variable. We show that a tricritical point on the smectic-A to hexatic-B phase transition line can be achieved under certain conditions. The theoretical prediction is found to be in good qualitative agreement with experimental results.