Structural study of an Al70Ni15Fe15 decagonal quasicrystal using high-angle annular dark-field scanning transmission electron microscopy

High-angle annular dark-field (HAADF) images of a melt-quenched Al70Ni15Fe15 decagonal quasicrystal have been taken using a scanning transmission electron microscope for the first time. We have found that the alloy is composed of 2-nm-diameter atom clusters with fivefold symmetry. We have also observed an inversion domain structure. A structural model has been constructed on the basis of the HAADF images and the fivefold cluster of the monoclinic tau(2)-Al13Co4 approximant model [Saitoh et al: J, Electron Microsc. 48 (1999) 105]. Antiphase shifts at domain boundaries have been observed directly for the first time. The present observation has verified the results of high-resolution electron microscopy (HREM) and the dark-field imaging technique obtained by Tsuda et al.