First principles investigation of the Al-V binary alloy system

Assessed alloy phase diagrams capture the consensus of experimental observation but often leave some details unresolved as far as the true thermodynamic stability of phases. The problems are especially acute at low temperatures, where equilibrium might not be achieved in the duration of the experiments. First principles calculations can help to resolve these questions. We illustrate this approach through investigation of the Al-V alloy system. Several structurally complex Al-rich phases fail to reach the convex hull of formation enthalpy, but they can be stabilized at finite temperature through entropic effects of partial site occupation and atomic vibrations. In the case of Al10V we treat the anharmonic vibrations of weakly bound "rattler" atoms that lead to anomalous low temperature heat capacity and thermal expansion. In the V-rich region, by enumerating all possible configurations in body-centered cubic supercells, we note potentially stable crystal structures that have not been reported experimentally.