Tricritical point in the incommensurate systems

The character of the incommensurate-commensurate phase transitions is discussed with the framework of the Landau-type theory. It is shown that the variation of the order parameter amplitude could induce an attractive interaction between phase solitons, and consequently lead to a discontinuous phase transition. In models relevant to corresponding transitions in ferroelectrics and liquid crystals, the tricritical point can thus be reached by varying the temperature and the anisotropy parameter.