An Icosahedral Quasicrystal and Its 1/0 Crystalline Approximant in the Ca–Au–Al System

Journal Article · Wed Sep 28 00:00:00 EDT 2016 · Inorganic Chemistry

DOI:https://doi.org/10.1021/acs.inorgchem.6b01636· OSTI ID:1347806

Pham, Joyce ^[1]; Kreyssig, Andreas ^[2]; Goldman, Alan I. ^[2]; Miller, Gordon J. ^[1]

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1. Iowa State Univ., Ames, IA (United States); Ames Lab., Ames, IA (United States)
2. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)

A new icosahedral quasicrystalline phase, CaAu_4.5–xAl_1.5+x [0.11 ≤ x ≤ 0.40(6); CaAu_4.4Al_1.6, a_QC = 5.383(4) Å, and Pm35], and its lowest-order 1/0 cubic crystalline approximant phase, CaAu_3+xAl_1–x [0 ≤ x ≤ 0.31(1); a = 9.0766(5)–9.1261(8) Å, Pa3(No. 205), and Pearson symbol cP40], have been discovered in the Ca-poor region of the Ca–Au–Al system. In the crystalline approximant, eight [Au_3–xAl_1+x] tetrahedra fill the unit cell, and each tetrahedron is surrounded by four Ca atoms, thus forming a three-dimensional network of {Ca_4/4[Au_3–xAl_1+x]} tetrahedral stars. Here, a computational study of Au and Al site preferences concurs with the experimental results, which indicate a preference for near-neighbor Au–Al interactions over Au–Au and Al–Al interactions. Analysis of the electronic density of states and the associated crystal orbital Hamilton population curves was used to rationalize the descriptions of CaAu_4.5–xAl_1.5+x [0.11 ≤ x ≤ 0.46(6)] and CaAu_3+xAl_1–x [0 ≤ x ≤ 0.31(1)] as polar intermetallic species, whereby Ca atoms engage in polar covalent bonding with the electronegative, electron-deficient [Au_3–xAl_1+x] tetrahedral clusters and the observed phase width of the crystalline approximant.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; National Science Foundation (NSF)
• Grant/Contract Number: AC02-06CH11357; AC02-07CH11358; DMR 10-05765
• OSTI ID: 1347806
• Journal Information: Inorganic Chemistry, Vol. 55, Issue 20; ISSN 0020-1669
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
group theory
electronic structure
gold
intermetallics
physical and chemical processes