Phase equilibria and thermodynamic limits for partitionless crystallization in the Al-La binary system

The thermodynamic properties and associated phase equilibria for the Al-La binary system are examined by combining first-principles calculations with a solution thermodynamics approach. In this analysis, the liquid phase is described using a three-species association model. The AlLa, Al7La3-C23, and low-temperature Al11La3-(alpha) phases are treated as stoichiometric compounds. All other phases are treated as solid solutions, where a single sublattice model is employed for terminal solids, and a two-sublattice model is employed for intermediate solids. The zero kelvin enthalpy of formation for each end-member phase is calculated from first principles. Model parameters are fitted using available experimental data, and the resulting phase diagram is reported over the full range of compositions in the binary system. Motivated by the potential thermodynamic implications related to the glass transition, particular attention is paid to the undercooled liquid, using a twostate model to describe the pure Al and La reference states. As an estimate of the partitionless limits for the crystallization process, the associated T0 (GS = GL) curves are determined and compared with reports of amorphous phase formation from the melt.