Unit-Cell Structure of Rapidly Cooled Al-Mn Alloys with Icosahedral Symmetry

An analysis of electron diffraction patterns is used to describe the structure of rapidly cooled Al-Mn alloys displaying icosahedral point-group symmetry and long-range orientational order. The underlying structure is provided by a lattice, the unit cell of which involves 32 atomic sites, which satisfy icosahedral symmetry. The appearance of the electron diffraction patterns can be understood by the coexistence of two independent three-dimensional lattices which can be found from this unit-cell structure.