The structure of type-II Al-Ni-Co decagonal quasicrystal studied by atomic-scale electron microscopic observations

The structure of an Al-Ni-Co decagonal quasicrystal, showing electron diffr action patterns called "type-II", in an Al71.5Ni12.5Co16 alloy, has been ex amined by high-angle annular detector dark-field scanning transmission elec tron microscopy and high-resolution transmission electron microscopy. Its s tructure has a columnar cluster of atoms with a decagonal section of about 2nm in diameter as a structural unit, and forms a heterogeneously aperiodic tiling of pentagonal and rhombic tiles in a two-dimensional arrangement of the columnar clusters. Translational arrangements of pentagons and rhombus es in the tiling can be observed locally. Also, the characteristic of a NaC l-type ordered arrangement of two kinds of columnar clusters of atoms, whic h have different orientations of pentagonal symmetry, is observed in the ti ling.