First-principles calculations for stability of atomic structures of Al-rich AlX (X=Sc–Zn) alloys, including AlMn quasicrystal: I. Solution energies of X in Al

The present and subsequent papers give ab initio data for the study of the stability of the atomic structures of Al-rich AlX (X–ScZn) alloys, including the AlMn quasicrystal. We consider the minority elements of alloys as impurities and divide the cohesive energies of AlX alloys into four components :(i) cohesive energies of Al and X; (ii) solution energies of X in Al; (iii) X–X interaction energies (IEs) in Al; (iv) many-body IEs of X-agglomerates in Al. In the present paper, we show the calculated results for (i), (ii), 1st-neighbor X–X IEs (one part of (iii)) and X–Vacancy IEs in Al and discuss quantitatively the fundamental features of the interatomic interactions characteristic to the Al-rich AlX alloys: (1) the sp–d interaction of X(=Sc–Ni) with neighboring Al atoms is stronger than the d-d interaction of the 1st-neighbor X–X; (2) Al atoms in the Al-rich AlX alloys may be rearranged easily on the condition that electron density does not change very much because of the strong free-electron character of Al sp-electrons. Both results suggest that the atomic structures of Al-rich AlX (X=Sc–Ni) are mainly determined by the medium-ranged and oscillating X–X interactions, due to the sp–d interaction of Al–X.