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Phase formation and structures of quasicrystals and approximants in the Zn–Mg–(Ti, Zr, Hf) system

✍ Scribed by S. Ohhashi; E. Abe; M. Tanaka; A.P. Tsai

Publisher
Elsevier Science
Year
2009
Tongue
English
Weight
715 KB
Volume
57
Category
Article
ISSN
1359-6454

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✦ Synopsis

The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn 84 Mg 9 Zr 7 and Zn 75 Mg 18 Zr 6 , respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn 77 Mg 18 Zr 5 . A similar tendency has been verified for the Zn-Mg-Hf system. No stable iQc was observed in the Zn-Mg-Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn-Mg-Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant.

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