Structure of a pentagonal quasicrystal in Al72.5Co17.5Ni10 studied by high-angle annular detector dark-field scanning transmission electron microscopy

The structure of a pentagonal quasicrystal, which has been called "basic Go -rich state of Al-Co-Ni decagonal quasicrystals", in an Al72.5Co17.5Ni10 al loy annealed at 900 degreesC for 40 hr has been studied by high-angle annul ar detector dark-field scanning transmission electron (HAADF-STEM). An obse rved HADDF-STEM image clearly shows that there exist columnar clusters of a toms with a decagonal section of about 2 nm in diameter as a structural uni t, and that the atomic clusters with the same orientation of pentagonal sym metry are arranged with a pentagonal quasiperiodic lattice. Thus, the basic Go-rich state can be concluded to be a pentagonal quasicrystal with a pent agonal quasiperiodic lattice.