Online ISSN : 1347-5320
Print ISSN : 1345-9678
Formation of Icosahedral Quasicrystal and Its 1/1 Crystal Approximant in Al-Pd-Sc System
Yeong-Gi SoKeiichi Edagawa
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2009 Volume 50 Issue 5 Pages 948-951


An icosahedral quasicrystal (i-phase) and its 1/1 crystal approximant (1/1-phase) have been found to form in Al-Pd-Sc system. The formation areas of the i-phase and the 1/1-phase are limited to very small areas around the compositions of Al54Pd30Sc16 and Al56Pd29Sc15, respectively. The valence electrons per atom ratio (e/a ratio) is calculated to be 2.10 for the i-phase of Al54Pd30Sc16. The 16 at% Sc concentration and ea=2.10, as well as the intensity profile of the measured X-ray diffraction spectrum, indicate that this i-phase can be classified into the Tsai-type: the Tsai-type i-phases found so far commonly contain an element having relatively large atomic size with 15–16 at% and have e/a within the range 2.0–2.15. The formation of the i-phase has also been found in a series of quaternary Al-Pd-Cu-Sc alloys with different compositions keeping 16 at%Sc and ea=2.10. This supports the fact that the two conditions are crucially important in the formation of this type of i-phase.

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© 2009 The Japan Institute of Metals and Materials
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