Structure of a metastable Al3Ni decagonal quasicrystal:: comparison with a highly perfect Al72Ni20Co8

We study the structure of a decagonal quasicrystalline phase formed in a rapidly-solidified Al3Ni alloy, by using electron diffraction and atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM). Electron diffraction patterns of the metastable Al3Ni phase reveal features quite similar to those of the stable Al72Ni20Co8 phase; a large number of reflections in the tenfold symmetry plane and no significant diffuse streaks in the twofold patterns, indicating a good quasiperiodic order of the phase. Z-contrast STEM imaging shows that the structure of the Al3Ni phase can be interpreted based on a decagonal atomic cluster column with broken tenfold symmetry, being basically isostructural with that of the Al72Ni20Co8 phase, Structural disorders are found to be significant at the core of the decagonal atomic clusters in the metastable Al3Ni decagonal phase. (C) 2002 Elsevier Science B.V. All rights reserved.