Structure of Al4Mn Decagonal Phase as a Penrose-Type Lattice

Abstract

Electron and X-ray diffractions from a metastable phase in an Al _79.5 Mn _20.5 alloy, formed by a rather slow quenching of the melt, have been consistently interpreted by the decagonal quasicrystalline phase (L. Bendersky: Phys. Rev. Left. 55 (1985) 1461). A structural model of the phase is proposed, in which two unit cells with the Penroserhombic prisms (edge length 4.30 Å and height 4.15 Å), containing five and three atoms, are packed in a plane, satisfying a face-matching rule to form a Penrose-type lattice with a ten-fold symmetry. These quasicrystalline layers stack periodically with an ordered modulation at every three layers.