NEUTRON DIFFRACTION STUDIES OF THE ICOSAHEDRAL PHASE OF Al-Mn ALLOYS

Powder neutron diffraction studies were performed on three icosahedral alloys of the aluminum manganese system containing 27, 30. and 34 weight percent manganese. All peaks were found at the angles consistent with the icosahedral indexing with a six-dimensional cubic lattice parameter of approximately 0.65 nm that decreased with increasing Mn content. The relative intensities differ significantly from those found for X-rays. The intensities are not consistent with a quasilattice consisting of the 3-dimensional Penrose tiling with a .46 nm edge length along the 5-fold axis. It is consistent with a 1.0 nm edge along the 3fold axis quasilattice node separation.