Re-optimization of the Mg–Sb system under topological constraints

Non-existing inverted miscibility gaps in the liquid phase at high temperatures, reappearance of the liquid phase at low temperatures or reappearance of a solid phase at elevated temperatures, and other “approximation phantoms” sometimes result from thermodynamic assessments. A method for struggling against such artifacts is proposed. The method is based on introducing a sufficiently dense mesh of knots (not related to experimental points utilized in the optimization) and ensuring that specific inequality conditions (topological constraints) governing the appearance of the phase diagram are satisfied in these knots. It is shown that the syntax of the language describing conditions and experiments in the PARROT module of Thermo-Calc is suitable for performing such optimization. The workability of the approach proposed is exemplified by carrying out a re-optimization of the Mg–Sb system.