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Chemical Disorder And Columnar Vacancies In Ideal Decagonal AL-NI-CO Quasicrystals

Published online by Cambridge University Press:  10 February 2011

Yanfa Yan
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
S. J. Pennycook
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
A.-P. Tsai
Affiliation:
National Research Institute for Metals, Tsukuba, Japan
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Abstruct

Atomic-resolution Z-contrast images provide conclusive evidence for chemical disorder in an ideal Al-Ni-Co quasicrystal. The so-called basic Ni-rich, high-temperature, quasiperiodic structure exhibits chemical disorder at the center of the 2 nm diameter clusters that involves both the Al and Ni(Co) atoms. The atomic structure of the 2 nm clusters is derived directly from the images and differs from previous models. The presence of closely-spaced, half-occupied atomic columns (or columnar vacancies) in specific rings within the clusters is directly observed. We propose that these columnar vacancies mediate the phason flips necessary for transformation to random tiling.

Type
Research Article
Copyright
Copyright © Materials Research Society 1999

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