Alloys: Atomic structure of the quasicrystal Al72Ni20Co8

Steinhardt et al. reported experimental evidence in support of the coverage model by presenting a structure for the high-perfection decagonal quasicrystal Al72Ni20Co8. The coverage model describes the decagonal quasicrystals by a single type of tile, a decagon, the basic 2-nm cluster of which is allowed to overlap so as to cover the surface. Although their Z-contrast image (also referred to as a high-angle annular dark-field image) supports the coverage model, we find that the atomic structure they propose for the decagon has significant shortcomings which are inconsistent with our Z-contrast images.