HAADF-STEM study of chemical ordering in Al-Pd-Sc 1/1-crystal approximant

Yeong Gi So*, Masahiro Nagao, Takuro Nagai, Koji Kimoto

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


The atomic structure of the Al 54Pd 31Sc 15 1/1-crystal approximant to the icosahedral quasicrystal has been studied using high-angle annular dark-field (HAADF) imaging in a scanning transmission electron microscopy (STEM). HAADF imaging directly reveals that the 1/1-phase has a periodic arrangement of Tsai-type atomic clusters, which consist of three successive shells with icosahedral symmetry as well as a disordered tetrahedron at the cluster center. In the 1/1-phase, the chemical ordering of Al and Pd is observed in the glue sites between the clusters, similar to that of Al and Au in the recently discovered Al 35Au 51Yb 14 1/1-phase, indicating a common structural feature of ternary Tsai-type approximants. Moreover, the preferential introduction of structural disorder into the second dodecahedral shell is observed in the HAADF images, which causes symmetry breaking of the 1/1-phase. On the basis of a comparison with the experimental and simulated images, a preliminary model for the atomic structure of the 1/1-phase is presented.

Original languageEnglish
Pages (from-to)7-11
Number of pages5
JournalJournal of Alloys and Compounds
Publication statusPublished - 2012 Dec 5
Externally publishedYes


  • Al-Pd-Sc alloy
  • Annular dark-field imaging
  • Crystal approximant
  • Icosahedral quasicrystal
  • Scanning transmission electron microscopy

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Materials Chemistry
  • Metals and Alloys


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