Structure of type I and type II modifications of Al–Co–Ni decagonal quasicrystals studied by HAADF-STEM technique

The structure of type I and type II modifications of Al–Co–Ni decagonal quasicrystals was studied by using the high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) technique. It was found that the quasi-unit-cell should be selected as columnar decagon of 3.2 nm in diameter and 0.82 nm in height, and its center consists of a bright circle with 0.76 nm of the outer diameter, indicating that atomic distribution in the quasi-unit-cell is disordered. Lattices obtained by connecting the centers of the atom clusters in HAADF images reveal that the lattice of the type I modification is rhombic Penrose tiling and the lattice of the type II is a mixture of the rhombic and pentagonal tilings. Namely, the lattice of the type II modification is a mixture of the lattices of the type I and S1 modifications.