Role of the triclinic Al(2)Fe structure in the formation of the Al(5)Fe(2)-approximant

The structural correspondence among the bcc, ordered-bcc B2, triclinic Al(2)Fe and approximant Al(5)Fe(2) structures have been examined on the basis of the experimentally obtained orientation relationship of (110)(bcc,B2) //(2 (2) over bar1)(Al2Fe) and [(1) over bar 11](bcc,B2) // N(241)(Al2Fe), where N(hkl) denotes the normal direction of the (hkl) plane. The formation of the triclinic Al(2)Fe structure from the bcc structure is directly associated with that of Al-Fe covalent bonds; that is, hybridization between Al and Fe atoms. The covalent bond formation results in the appearance of decagonal-like atomic arrangements in the Al(2)Fe structure, which are similar to those in the approximant Al(5)Fe(2) structure.