High-angle annular dark-field (HAADF) images of an Al72Ni20Co8 decagonal quasicrystal and monoclinic Al13Fe4 and τ2-inflated Al13Co4 approximants have been presented. We found that a 2 nm atom cluster of Al72Ni20Co8, which have been believed to be tenfold so far, has no tenfold symmetry. A new structural model of Al72Ni20Co8 has been constructed on the basis of the HAADF images and the structure of monoclinic Al13Fe4 approximant. We have found that the monoclinic Al13Fe4 and τ2-inflated Al13Co4 approximants are composed of the same basic structure of a pentagonal atom cluster with an edge length of 0.47 nm. We have also found that a fivefold atom-cluster with a 2 nm diameter exists in τ2-Al13Co4, which was observed in decagonal quasicrystals of Al-Ni-Fe, Al-Ni-Co, Al-Cu-Co and Al-Co by high-resolution electron microscopy. A structural model of τ2-inflated Al13Co4 is constructed on the basis of the convergent-beam electron diffraction symmetry, HAADF images and the structure of monoclinic Al13Fe4.
|Number of pages||6|
|Journal||Materials Research Society Symposium Proceedings|
|Publication status||Published - 1999|
|Event||Proceedings of the 1998 MRS Fall Meeting - The Symposium 'Advanced Catalytic Materials-1998' - Boston, MA, USA|
Duration: 1998 Nov 30 → 1998 Dec 3