2001 Volume 42 Issue 6 Pages 1146-1148
The structure of a pentagonal quasicrystal, which has been called “basic Co-rich state of Al–Co–Ni decagonal quasicrystals”, in an Al72.5Co17.5Ni10 alloy annealed at 900°C for 40 hr has been studied by high-angle annular detector dark-field scanning transmission electron (HAADF-STEM). An observed HADDF-STEM image clearly shows that there exist columnar clusters of atoms with a decagonal section of about 2 nm in diameter as a structural unit, and that the atomic clusters with the same orientation of pentagonal symmetry are arranged with a pentagonal quasiperiodic lattice. Thus, the basic Co-rich state can be concluded to be a pentagonal quasicrystal with a pentagonal quasiperiodic lattice.