Formation of an ordered intermetallic phase from a disordered solid solution - A study using first-principles calculations in Al-Li alloys

The formation of the ordered Li-2 phase in Al-Li binary solid solutions has been studied using first-principles electronic structure calculations in conjunction with the static concentration wave model. The effective multisite interactions have been determined by using Connolly-Williams prescription in the tetrahedron-octahedron (TO) cluster approximation for the f.c.c. lattice. The resulting Landau plots (free energy versus order parameter) have pointed out the temperatures below which instabilities with respect to ordering develops. Free energy-composition plots have been used for identifying the positions of the phase boundaries and of the critical spinodal. The results of this theoretical investigation have been presented in the form of a phase diagram in which different instability lines have been marked. Copyright (C) 1997 Acta Metallurgica Inc.