Interatomic Potentials and Defect Energetics in Dilute Alloys

Effective interatomic potentials for impurities in aluminum have been constructed according to pseudopotential theory. Based on a local model potential, impurity valence and size factors are defined and their effects on the potential discussed. With these potentials, detailed calculations based on a Green's function lattice statics method are made for the impurity-vacancy binding energy and the difference in diffusion activation energies for an impurity and a host atom. Within the range of valence and size factors studied, it is found that the binding energy is generally small and depends primarily on the valence rather than the size, whereas the migration energy shows larger increases with both valence and size factors. Contributions from the lattice relaxation energies are important, particularly for impurity migration. The results can account satisfactorily for the experimental data of nontransition-metal impurities, but less so for the noble-metal impurities. Dielectric screening of the ion by the conduction electrons is important in determining the potential and must be properly accounted for in calculations of the energetics for impurities.