ALCHEMI study of an Al72Ni20Co8 decagonal quasicrystal

Two-dimensional channelling patterns, derived from variations in characteri stic X-ray emission rates as a function of incident electron beam orientati on, have been recorded from an Al72Ni20Co8 decagonal quasicrystal for the f irst time. These channelling patterns indicate that the Al and transition m etal atoms occupy different sets of sublattice sites, and that (to a good a pproximation) both Ni and Co atoms randomly occupy a similar set of sublatt ice sites, i.e. they are mutually disordered. This is shown to support the view that the structure of this alloy is determined primarily by the number of electrons per atom; e/a.