Campus Units

Chemistry, Ames Laboratory

Document Type

Article

Publication Version

Published Version

Publication Date

2008

Journal or Book Title

Inorganic Chemistry

Volume

47

Issue

17

First Page

7651

Last Page

7659

DOI

10.1021/ic800694j

Abstract

Two crystalline approximants (ACs) and their corresponding icosahedral quasicrystal (i-QC) are obtained in the Ca−Au−Ga system through conventional solid-state exploratory syntheses. Single crystal structural analyses reveal that the 1/1 AC, Ca3AuxGa19-x (x = ∼ 9.3−12.1) [Im3̅, a = 14.6941(6)−14.7594(6) Å], has the empty cubes in the prototypic YCd6 (= Y3Cd18) now fully occupied by Ga, resulting in a 3:19 stoichiometry. In parallel, the distorted cubes in the 2/1 AC, Ca13Au57.1Ga23.4 [Pa3̅, a = 23.9377(8) Å] are fully or fractionally occupied by Ga. The valence electron count per atom (e/a) for the 2/1 AC (1.64) is smaller than that over the 1/1 AC composition range (1.76−2.02), and the e/a of the Ca15.2Au50.3Ga34.5 i-QC, 1.84, is somewhat distant from typical values for Tsai-type i-QCs (∼ 2.0). Comparisons of the gallium results with the corresponding In phases suggest that the structural differences result mainly from size rather than electronic factors. The 1/1 and 2/1 appear to be thermodynamically stable on slow cooling, as usual, whereas the i-QC isolated by quenching decomposes on heating at ∼660 °C, mainly into 2/1 AC and Ca3(Au,Ga)11. Calculations of the electronic structure of 1/1 AC suggest that the Fermi sphere−Brillouin zone interactions remain important for the Ca−Au−Ga i-QC.

Comments

This is an article from Inorganic Chemistry 47 (2008): 7651, doi: 10.1021/ic800694j. Posted with permission.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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