A thermodynamic approach to T-P phase diagrams of substances in liquid and amorphous states

The metastable phase equilibria of substances in the disordered, liquid or amorphous, state are considered in T-P coordinates. Application of the thermodynamic model of pseudo-binary solutions is illustrated by means of calculated metastable T-P phase diagrams of water, carbon, and semiconducting compounds, GaSb and Ga38Sb38Ge24. All calculated diagrams include the equilibrium lines between the disordered phases terminating at the critical points and the stability boundaries of these phases, the spinodals. Depending on the mutual disposition of the elements of the stable and metastable T-P diagrams, two additional lines of metastable equilibria between the crystalline high-pressure phase and each of the metastable disordered phases can appear. These lines terminate at the points of intersection with spinodals. These special points are denoted as pseudo-critical points. A combined analysis of the stable and metastable diagrams gives a reasonable interpretation of the experimental data on the phase transformations and on the nature of the anomalous properties of the substances in question as well as allowing prediction of some new effects.