Ab-initio Calculations for Interatomic Interactions in Al-rich AlX (X=Sc-Zn) Alloys and Atomic Structures

Abstract

There are many kinds of exprimenatally-known atomic structures (ASs) for Al-rich AlX (X=Sc-Zn) alloys, depending on X. The ASs for Al₃Sc and Al₃V are L1₂ and DO₂₂, respectively, while the local ASs for the quasicrystal Al₈₀Mn₂₀ is Mackay icosahedron. For X=Cu and Zn, the Al_1-cX_c (c<0.05) alloys have a phase decomposition, but the shapes of Cu- and Zn-precipitations are very different. In order to elucidate the interactions characteristic of the Al-rich AlX alloys and the micromechanism of stability of the above-mentioned ASs, we give systematic ab-initio calculations for the two-body and many-body(MB) interaction energies (IEs) of X atoms in Al. The calculated results for X=3d elements show; (1) the Al-X pairs are very stable because of the strong sp-d interactions (INTs) of X atoms with the neighboring Al atoms; (2) the n th-MB IEs of X atoms rapidly decrease with the increase of n; (3) The X-X INTs in Al show the distance dependence of Friedel-type oscillation because the X-X INTs beyond the 2nd-neighbor distance are mediated by free-electron-like sp electrons of Al. The chemical trend of ASs of the above-mentioned alloys is explained by using the calculated X-X IEs.