Structure of τ2-Al3Co, a Monoclinic Approximant of the Al–Co Decagonal Quasicrystal

  • K. Sugiyama
  • A. YasuharaEmail author
  • K. Hiraga


The structure of the approximant τ 2-Al3Co (P2/m: a=3.9831(3) nm, b=0.8127(1) nm, c=3.2182(3) nm, and β=108.03(1)), associated with the decagonal quasicrystals with a period of 0.8 nm, was analyzed using a high-angle annular detector dark-field (HAADF) observation with Cs-corrected scanning transmission electron microscopy (STEM). The HAADF-STEM image clearly showed the arrangement of individual Co atoms as bright dots. The contrast among the atoms in the lattice led to an image of the fundamental structure of the τ 2-Al3Co phase, composed of an ordered arrangement of pentagonal columnar units with edge lengths of 0.47 nm. The arrangements of atoms in the columnar units were quantitatively determined by single crystal X-ray diffraction (XRD). The results demonstrate that the pentagonal columnar units form common tiles in the shape of a squashed hexagon, a pentagonal star, and a crown. Among the tiles, the pentagonal star composed of 10 pentagonal units was similar to that found in the W-(AlNiCo) approximant for the Al–Ni–Co decagonal quasicrystal (DQC).


Edge Length Scanning Transmission Electron Microscopy Isotropic Displacement Parameter Decagonal Quasicrystal Puckered Layer 
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A part of this work was supported by a Grant-in-Aid for Challenging Exploratory Research (22656152) from the Japan Society for the Promotion of Science (JSPS).


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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Institute for Materials ResearchTohoku UniversitySendaiJapan
  2. 2.EM Application Group, EM Business UnitJEOL Ltd.AkishimaJapan

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