Development of the Ca-Au-In Icosahedral Quasicrystal and Two Crystalline Approximants: Practice via Pseudogap Electronic Tuning
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Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.
For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.
The Department of Chemistry seeks to provide students with a foundation in the fundamentals and application of chemical theories and processes of the lab. Thus prepared they me pursue careers as teachers, industry supervisors, or research chemists in a variety of domains (governmental, academic, etc).
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The Department of Chemistry was founded in 1880.
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1880-present
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- College of Liberal Arts and Sciences (parent college)
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Abstract
Electronic tuning and syntheses to gain the icosahedral quasicrystal (i-QC) (Ca14.1(2)Au44.2(8)In41.7(7), e/a = 1.98) and two approximant crystals (ACs) are reported. The tuning was derived from Na2Au6In5, another cubic Mg2Zn11-type structure, for which the Fermi level (e/a = 1.77) should tune to a calculated pseudogap (e/a = 2.02) under a rigid band assumption. The 1/1 AC, Ca3Au12.2(1)In6.3(2) (e/a = 1.73), crystallizes in space group Im3̄, with a = 15.152(2) Å, Z = 8, and the 2/1 AC, Ca12.6(1)Au37.0(2)In39.6(6) (e/a = 2.01), in Pa3̄, with a = 24.632(3) Å , Z = 8. Both have substantially fixed compositions according to lattice dimensions. Structure analyses reveal that both ACs contain triacontahedral clusters as the basic building blocks at the body-centered and primitive cubic unit cell levels, respectively. Densities-of-states (DOS) analyses for the 1/1 AC structure reveal a pseudogap at e/a = 2.00, close to the point at which the i-QC was predicted and experimentally tuned. Phase relationships of the ACs and the i-QC are reported according to DTA, XRD, and temperature-dependent XRD measurements. The QC is thermodynamically metastable below ∼500 °C.
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This is an article from Journal of the American Chemical Society 129 (2007): 6789, doi: 10.1021/ja069143x. Posted with permission.