ALCHEMI study of an S1-type superlattice-ordered decagonal quasicrystal of Al70Ni18Co12

Electron channeling patterns, which display the intensity variation of characteristic X-ray emission as a function of incident beam orientation, have been taken from an S1-type superlattice-ordered decagonal quasicrystal of Al70Ni18Co12, which shows diffuse streaks on and halfway between Bragg spot layers perpendicular to the decagonal direction in the electron diffraction patterns. The channeling patterns show that Al atoms and transition metals occupy different sublattice sites, and that both Ni and Co atoms randomly occupy the same sublattice sites, that is, they are disordered. This indicates that the origin of the diffuse streaks is not related to a chemical order between Ni and Co, but is caused only by a topological order, such as a small displacement of atoms.