Tricritical behavior of the smectic-A to smectic-C* transition

A phenomenological Landau-like theory is presented, which describes the tricritical behavior of the smectic-A to smectic-C-* transition in a liquid crystal mixture. The influence of the concentration on this transition is discussed by varying the coupling between the concentration variable and the order parameters. It was observed from the theoretical calculations that for a particular value of the concentration, the first order smectic-A to smectic-C-* transition becomes second order at a tricritical point. Calculations based on this model agree qualitatively with experiment.