Structure of quasicrystalline approximant phase in the Al[sbnd]Pd[sbnd]Mn system

Abstract

The structure of an orthorhombic phase (ξ′ phase) with Al_73·5Pd₂₂₄Mn_4·1 composition was solved by applying the direct methods and refined by a least-squares procedure. The space group is Pnma and the magnitudes of cell parameters are a = 23·541 Å, b = 16·566 Å and c = 12·339 Å. The final reliability factor is R = 0·072 for 3419 independent reflections. The structure is made up of partial Mackay icosahedra in which the Pd atoms form icosahedra centred on Mn atoms. These central Mn atoms are located at the vertices of flattened hexagons arranged in quincunx. The ξ′ phase is nearly isomorphic to the Al₃Pd structure and has a layer structure consisting of flat and puckered layers similar to what is found in Al₃Mn and Al₁₃Fe₄.