Phenomenological theory of phase diagrams with multicritical points

The breakup of multicritical points is studied in detail within the phenomenological theory of second-order phase transitions for a thermodynamic potential invariant with respect to the C _3v (3m) group of transformations. The general conditions of this breakup are obtained and possible types of derived diagrams are plotted from a parent phase diagram containing a multicritical point. Examples of experimental phase diagrams are given that qualitatively confirm the results from theoretical and computer simulations of phase equilibria.