Campus Units

Chemistry, Ames Laboratory

Document Type

Article

Publication Version

Published Version

Publication Date

2010

Journal or Book Title

Journal of the American Chemical Society

Volume

132

Issue

16

First Page

5662

Last Page

5671

DOI

10.1021/ja100250d

Abstract

Synthetic explorations in the CaAu5−CaAu4Bi−BiAu2 system at 400 °C reveal five separate solid solution regions that show three distinct substitution patterns in the CaAu5 parent: (I) CaAu4(Au1−mBim) with 0 ≤ m ≤ 0.15(1), (II) 0.33(1) ≤ m ≤ 0.64(1), (III) 0.85(4) ≤ m ≤ 0.90(2); (IV) (Ca1−rAur)Au4(Bi1−sAus) with 0 ≤ r ≤ 0.39(1) and 0 ≤ s ≤ 0.12(2); (V) (Ca1−pqAupBiq)Au4Bi with 0.09(2) ≤ p ≤ 0.13(1) and 0.31(2) ≤ q ≤ 0.72(4). Single crystal X-ray studies establish that all of these phase regions have common cubic symmetry F4̅3m and that their structures (MgCu4Sn-type, an ordered derivative of MgCu2) all feature three-dimensional networks of Au4 tetrahedra, in which the truncated tetrahedra are centered and capped by Ca/Au, Au/Bi, or Ca/Au/Bi mixtures to give 16-atom Friauf polyhedra. TB-LMTO-ASA and -COHP calculations also reveal that direct interactions between Ca−Au and Ca−Bi pairs of atoms are relatively weak and that the Bi−Au interactions in the unstable ideal CaAu4Bi are antibonding in character at EF but that their bonding is optimized at ±1 e. Compositions between the five nonstoichiometric phases appear to undergo spinodal decompositions. The last phenomenon has been confirmed by HRTEM, STEM-HAADF, EPMA, and XRD studies of the nominal composition CaAu4.25Bi0.75. Its DTA analyses suggest that the phases resulting from spinodal decomposition have nearly the same melting point (∼807 °C), as expected, and that they are interconvertible through peritectic reactions at ∼717 °C.

Comments

This is an article from the Journal of the American Chemical Society 132 (2010): 5662, doi: 10.1021/ja100250d. Posted with permission.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

Share

COinS