General Results Al-Rich CMAs Including Approximants

This has been interpreted as evidence for electron localization, which has also been proposed to explain anomalous transport in bulk QCs [169, 191, 192]. 

General Results Al-Rich CMAs (Including Approximants) 

The study of QC surfaces has led to interest in the surfaces of related CMAs. QCs typically exist in a narrow composition region of the phase diagram due to the Hume-Rothery constraint of specific valence electron to atom ratio, which is related to electronic stabilization of QCs [196-198]. In the neighborhood of this composition region, phases with giant unit cells and local atomic order related to that of the QC can usually be found. The surfaces of these approximant phases offer the possibility of exploring surface structure and properties as a function of increasing complexity, which can be most simply defined in terms of atoms f er unit cell. 

One CMA system intermediate between periodic crystals and approximant CMAs is g-Al4Cu9(110) [147-149]. This is a simple cubic (SC) phase with 54 atoms in the unit cell, and while not strictly an approximant, it is closely linked to QCs. Its formation on a surface was first observed following annealing of a thin Cu film deposited on the 5-f surface of i-Al-Pd-Mn [200], and the surface was later studied in more detail using STM and LEED [147]. Duguet et al. [148] suggested its use as an interfacial buffer layer between quasicrystaUine and periodic materials and demonstrated its formation on i-Al-Cu-Fe. Recently, the (110) surface of the bulk material has also been studied [149]. The results from aU of these studies are consistent with the general conclusions for approximant surfaces outlined earlier. 

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