Search

The realm of Tsai-type (YCd6-type) quasicrystals(QCs) and their approximants(ACs) continues to expand to the east in the periodic table. The heavy tetrel Sn is now one of the major components in the new Ca15.0(5)Au60.0(4)Sn25.0(2)(atom %) icosahedral QC and in the corresponding 1/1 and 2/1 ACs. (The 2/1 AC with Yb is also established.) Single-crystal X-ray diffraction on a 1/1 AC gives the refined formula of Ca3Au14.36(3)Sn4.38(5), in space group lm3, a = 15.131(1) Å, whereas a representative 2/1 AC gives Ca13Au47.2(1)Sn28.1(1), Pa3 and a 24.444(1) Å. Both ACs contain five-shell multiply endohedral triacontahedral clusters as the common building blocks, as in the parent structure of YCd6. The 2/1 AC also contains four Ca2-dimer-centered prolate rhombohedra (PRs) in the unit cell. The long-range order between triacontahedra and PRs in the 2/1 AC is the same as those in Bergman-type 2/1 ACs. A TB-LMTO-ASA calculation on an art ideal 1/1 AC model reveals a shallow pseudogap in the total densities-of-states data around the Fermi energy, as expected. The depth of the pseudogap is considerably enhanced through interactions between the Ca 3d states and s and p stales of Au and Sn. [ABSTRACT FROM AUTHOR]

Two La[sub3]AI[sub11] type derivatives have been discovered in the Ca-Au-Ge system and structurally characterized by single-crystal X-ray diffraction. Compositions Ca[sub3]Au[sub7.16(6)]Ge[sub3.84(6)] (1) and Ca[sub3]Au[sub7.43(9)]Ge[sub3.57(9)] (2) lie within a non-centric Imm2 phase region with a ≈ 4.40 Å, b ≈ 13.06 Å, C ≈ 9.60 Å. The Au-richer and electron-poorer Ca[sub3]Au[sub7.50(1)]Ge[sub3.50(1)] (3) and Ca3Au8Ol(l)Ge2.99(l) (4) occur within a centric Pnnm phase region with a ≈ 9.50 Å, b ≈ 13.20 Å, c ≈ 4.43 Å. Both phases contain complex [Au,Ge][sub11][sup6] polyanionic networks made up of hexagonal and pentagonal prisms that are filled with the electropositive Ca atoms. Both 3:11 phases represent opposed 1 x 3 x 1 superstructure distortions of CaAu[sub2]Ge[sub2] (ThCr[sub2]Si[sub2] type, 14/mmm), the structure of which has also been re-determined in this work. Linear muffin-tin-orbital (LMTO) calculations reveal that the symmetry variations induced by changes of the Au contents in the present 3:11 phases are consequences of bonding and structural optimizations. The hypothetical "CaAu[sub2.33-2.67]Ge[sub1.33-1.00]◻[sub00.33]" compositions, which are close to those of 1-4, follow through creation and elimination of vacancies within the electronegative networks of CaAu[sub2]Ge[sub2]. [ABSTRACT FROM AUTHOR]

The EuAuGe-type CaAuSn phase has been synthesized and single-crystal X-ray diffraction analysis reveals that it has an orthorhombic symmetry (space group Imm2), with a = 4.5261 (7) Å, b = 7.1356 (11) Å and c = 7.8147 (11) Å. The structure features puckered layers that are connected by homoatomic Au-Au and Sn-Sn interlayer bonds. This structure is one of the two parent structures of its high-temperature polymorph ( ca 873 K), which is an intergrowth structure of the EuAuGe- and SrMgSi-type structures in a 2:3 ratio. [ABSTRACT FROM AUTHOR]

The low-temperature form of CaAuSn is prepared by heating stoichiometric amounts of the elements (sealed Ta ampoule in evacuated silica tube, 1073 K, 1 d; cooling to 773 K with a rate of 2 K/h). [ABSTRACT FROM AUTHOR]

Sr2Au6(Au3-xMx) (M: Zn, Ga) samples with 1 ≤ x ≤ 3 are prepared by reaction of the elements (sealed Ta tubes, 800 °C, 10 h). [ABSTRACT FROM AUTHOR]

The title intermetallic phases are prepared from the elements at 700-800 °C for 6-10 h followed by annealing at 400-500 °C for 7-14 d. [ABSTRACT FROM AUTHOR]

Sr3Au8Sn3 is prepared by melting stoichiometric amounts of the metals (sealed Ta tube in evacuated silica jackets, 800 °C, 6 h; annealing at 400 °C, 1 week). [ABSTRACT FROM AUTHOR]

The first Na-containing icosahedral quasicrystal Na13Au12Ga15 is synthesized from mixtures of the elements in welded Ta tubes under Ar (750 °C, 3-5 h, followed by annealing at 350 °C for 3-5 d). [ABSTRACT FROM AUTHOR]