FEASIBILITY OF PHASE DETERMINATION IN QUASI-CRYSTALS AND MICROCRYSTALS BY MEANS OF MULTIPLE BRAGG SCATTERING

Multiple diffraction experiments have been performed on a microcrystal and a quasicrystal of the Al - Cu - Fe alloy for the purpose of extra cting phase information. The microcrystal used in this work is a twinn ed rhombohedral crystal exhibiting overall icosahedral symmetry. The e xperiments are performed by rotating the specimen around the scatterin g vector, (psi-scans) and by observing the peaks due to the Renninger effect, and the asymmetric features on the wings of the peaks, source of phase information. By fitting theoretical plots to the experimental psi-scans we conclude, within the resolution limits of this experimen t, that the atomic arrangement in a microcrystal seems to be different from that of the corresponding quasicrystal and that the structure ma y be centrosymmetric. The measurements on the quasicrystal support a p revious finding that the structure is not centrosymmetric.