Structural disorder of the atom cluster in a highly-ordered decagonal quasicrystal of Al₇₂Ni₂₀Co₈

Abstract

Spherical-aberration-corrected high-resolution transmission electron microscopy observation has been carried out for a highly ordered decagonal quasicrystal of water-quenched Al₇₂Ni₂₀Co₈. Atom clusters with a 2 nm diameter, which are considered to be basic structural motifs of the present alloy, show triangular shaped atomic arrangements in the central part, as observed previously by high-angle annular dark-field scanning transmission electron microscopy. The triangular arrangement is not identical for all the atom clusters but varies from cluster to cluster, although the orientational order of the triangles agrees well with the quasiperiodic order. The present results indicate that decagonal Al₇₂Ni₂₀Co₈ with a highly perfect quasiperiodic order contains a relatively large amount of structural disorder inside the atom cluster, which may be caused by a local relaxation to form the highly-ordered quasiperiodic arrangement of the atom-cluster.

Acknowledgements

The authors are thankful to Dr. M. Haider and his colleagues of CEOS GmbH for technical support. The present study is partially supported by special coordination grants of “Active nano characterization” and “Nano-CMOS”, grants-in-aid for scientific research (A) as “Fluctuation of structures and electronic states” (no. 17201022). One of the authors (A.P. Tsai) is grateful for the support by Core Research for Evolutional Science and Technology of Japan Science and Technology Corporation.