Ho arrangement in the Zn6Mg3Ho icosahedral quasicrystal studied by atomic-resolution Z-contrast STEM

The atomic structure of the Zn,Mg,Ho icosahedral quasicrystal has been stud ied by high-angle annular dark-field scanning transmission electron microsc opy (HAADF-STEM) with Z-contrast (Z: atomic number). We demonstrate that in particular Z-contrast imaging is quite powerful for specifying heavy atom positions in the quasicrystalline compound, as shown by a comparison with h igh-resolution phase-contrast imaging. It is confirmed that the observed Z- contrast images are fairly well explained by the projected potential of onl y the Ho atomic arrangement, which was recently proposed by X-ray diffracti on analysis; Ho occupies an even-body-center site of the 3-dimensional Penr ose lattice. Consequently, the present direct structural observation strong ly supports the validity of the proposed Ho site.