Local constriction around minor elements in Al86Ni7X1Y6 metallic glass (X: Ag, Au, Pt)

Abstract

The local structure around Ag, Au and Pt atoms in Al86Ni7X1Y6 (X: Ag, Au, Pt) bulk amorphous alloy was studied by X-ray absorption spectroscopy. Strong bond-shortening and a concomitant reduction of Al nearest neighbors around Ag, Au and Pt atoms compared to a dense random packing of hard spheres (based on the metallic radii of the elements) were observed suggesting strong covalent (Ag, Au, Pt) — Al bonds. This is ascribed to charge transfer from first-shell Al atoms to the X atoms resulting in s–p hybridization of the bonds. This causes opposite changes of the effective radii of X and Al atoms. Our results suggest that models using the metallic radii of elements are not appropriate to describe Al-based metallic glasses which contain Ag, Au or Pt atoms.