Lithiation-Induced Zinc Clustering of Zn3, Zn12, and Zn18 Units in Zintl-Like Ca∼ 30Li3+ xZn60–x (x= 0.44–1.38)

Zinc clusters are not common for binary intermetallics with relatively low zinc content, but this work shows that zinc clustering can be triggered by lithiation, as exemplified by Ca∼30Li3+xZn60–x, P6/mmm, Z = 1, which can be directly converted from CaZn2. Two end members of the solid solution (x = 0.44 and 1.38) were established and structurally characterized by single-crystal X-ray diffraction analyses: Ca30Li3.44(6)Zn59.56(6), a = 15.4651(9) Å, c = 9.3898(3) Å; Ca30.45(2)Li4.38(6)Zn58.62(6), a = 15.524(3) Å, c = 9.413(2) Å. The structures of Ca∼30Li3+xZn60–xfeature a condensed anionic network of Zn3 triangles, lithium-centered Zn12 icosahedra, and arachno-(Zn,Li)18 tubular clusters that are surrounded respectively by Ca14, Ca20, and Ca30polyhedra. These polyhedra share faces and form a clathrate-like cationic framework. The specific occupation of lithium in the structure is consistent with theoretical “coloring” analyses. Analysis by the linear muffin-tin orbital (LMTO) method within the atomic sphere approximation reveals that Ca∼30Li3+xZn60–x is a metallic, Zintl-like phase with an open-shell electronic structure. The contribution of Ca–Zn polar covalent interactions is about 41%

Mg35Cu24Ga53: A Three-Dimensional Cubic Network Composed of Interconnected Cu6Ga6 Icosahedra, Mg-Centered Ga16 Icosioctahedra, and a Magnesium Lattice

Single-crystal X-ray structural determinations for the Mg35.12(4)Cu24Ga53.58(6) and Mg35.6(4)Cu24Ga52.66(6) refined compositions (Fd3̄m, Z = 4) reveal empty (Cu,Ga)12 icosahedra and centered MgGa16 icosioctahedra that are interconnected at every vertex to a compact three-dimensional anion network. A small range of variable occupancy exists on one of three Ga and one of four Mg positions. The clusters are well-bonded and held in different sized cavities, in which they are also directly bonded to a Mg cation network. The two networks thus interpenetrate each other, and there are no spacers. The new phase is isostructural with K39In80, K17In41, and the electron-poorer Na35Cd24Ga56, all of which contain clathrate-II-type cation frameworks. Electron counting using the classic (MO-based) cluster assignments indicates that the refined structure is substantially ideal and closed-shell. The symmetry of the present structure does not suggest a ready conversion to an icosahedral quasicrystal or its approximants

Exploratory Syntheses and Structures of SrAu4.3In1.7 and CaAg3.5In1.9: Electron-Poor Intermetallics with Diversified Polyanionic Frameworks That Are Related to YCd6-Type Quasicrystal

The phase regions around quasicrystals and approximants (QC/ACs) are rich pools for electron-poor intermetallics with novel, complex structures, and bonding patterns. The present SrAu4.30(1)In1.70(1) (1) and CaAg3.54(1)In1.88(1) (2) were synthesized through chemical tunings of the model CaAu4In2 (YCd6-Type) AC. Single crystal X-ray diffraction analyses reveals that crystal 1 has Pnma (CeCu6-type) symmetry, with a = 9.102(1) Å, b = 5.6379(9) Å, and c = 11.515(2) Å. The building block in 1 is a 19-vertex cluster Sr@Au9In4M6 (M = Au/In), which vividly mimics Ca@(Au,In)18 in Ca3Au12.4In6.1 (YCd6-type) in geometry. These clusters aggregate into one-dimensional columns extending along the b axis. Crystal 2 (P6/mmm, a = 20.660(3) Å, c = 9.410(2) Å) is closely related to Na26Cd141 (hP167) and Y13Pd40Sn31 (hP168), which are differentiated by the selective occupation of Wyckoff 1a (0 0 0) or 2d (1/3 2/3 1/2) sites by Cd or Pd. Crystal 2 adopts the Na26Cd141 structure, but the 1a site is split into two partially occupied sites. The synergistic disorder in the hexagonal tunnels along c is a major property. The valence electron count per atom (e/a) values for 1 and 2 are 1.63 and 1.74, respectively, the lowest among any other ternary phases in each system. These values are close to those of ACs in the Ca–Au–M (M = Ga, In) systems. Electronic structures for both are discussed in terms of the results of TB-LMTO-ASA calculations

Ca14Au46Sn5: a “Colored” Gd14Ag51-type Structure Containing Columns of Well-Differentiated Hexagonal Gold Stars

A novel hexagonal phase discovered near the Ca15Au60Sn25 quasicrystal and its cubic approximants (ACs) was synthesized by means of high-temperature solid-state reactions. Single-crystal structural analyses show that this is a Gd14Ag51 isotype with composition within the range Ca14Au45.56(4)−46.67(4)Sn5.14(3)−4.14(3), space group P6/m (No. 175), and lattice parameters a = 12.763(3)−12.879(3) Å and c = 9.326(3)−9.3815(4) Å. In this phase, Sn mixes with Au in two of seven anionic sites to give a strong coloring that generates a narrow honeycomb-like Au/Sn template, in which sizable columns of hexagonal Au stars are confined. This phase transforms into the cubic 2/1 AC phase through a peritectic reaction at ∼678 °C. The valence electron count per atom (e/a) of the present phase is in the range 1.41−1.45. However, it does not appear to follow a Hume−Rothery mechanism

Li14.7Mg36.8Cu21.5Ga66: An Intermetallic Representative of a Type IV Clathrate

Synthetic explorations in the quaternary Li−Mg−Cu−Ga system yield the novel intermetallic Li14.7(8)Mg36.8(13)Cu21.5(5)Ga66 [P6̅m2, Z = 1, a = 14.0803(4) Å, c = 13.6252 (8) Å] from within a limited composition range. This contains a unique three-dimensional anionic framework consisting of distinct interbonded Ga12 icosahedra, dimerized Li@(Cu,Mg)10Ga6 icosioctahedra, and 15-vertex Li@(Cu,Mg)9Ga6 and Li@Cu3Ga12 polyhedra. These polyhedral clusters are hosted by M20 (512), M24 (51262), and M26 (51263) (M = Li/Mg) cages, respectively. The geometries and arrangements of these cages follow those in known type IV clathrate hydrates

M3(Au,Ge)19 and M3.25(Au,Ge)18 (M = Ca, Yb): Distinctive Phase Separations Driven by Configurational Disorder in Cubic YCd6-type Derivatives

Exploratory syntheses in the M−Au−Ge (M = Ca, Yb) systems have led to the discovery of two cleanly separated non-stoichiometric phases M3Au∼14.4Ge∼4.6 (I) and M3.25Au∼12.7Ge∼5.3 (II). Single crystal X-ray studies reveal that both (space group Im3̅) feature body-centered-cubic packing of five-shell multiply endohedral clusters that resemble those in the parent YCd6 (= Y3Cd18) and are akin to approximate phases in other quasicrystal systems. However, differences resulting from various disorders in these are distinctive. The innermost cluster in the M3Au∼14.4Ge∼4.6 phase (I) remains a disordered tetrahedron, as in the YCd6 parent. In contrast, its counterpart in the electron-richer M3.25Au∼12.7Ge∼5.3 phase (II) is a “rattling” M atom. The structural differentiations between I and II exhibit strong correlations between lattice parameters, cluster sizes, particular site occupancies, and valence electron counts

Development of the Ca-Au-In Icosahedral Quasicrystal and Two Crystalline Approximants: Practice via Pseudogap Electronic Tuning

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

A study of the Phase Mg2Cu6Ga5, Isotypic with Mg2Zn11. A Route to an Icosahedral Quasicrystal Approximant

The new title compound was synthesized by high-temperature means and its X-ray structure refined in the cubic space group Pm3̄, Z = 3, a = 8.278(1) Å. The structure exhibits a 3-D framework made from a Ga14 and Mg network within which large and small cavities are occupied by centered GaCu12 icosahedral and Cu6 octahedral clusters, respectively. The clusters are well bonded within the network. Electronic structure calculations show that a pseudogap exists just above the Fermi energy, and nearly all pairwise covalent interactions remain bonding over a range of energy above that point. Analysis suggests that the compound is hypoelectronic with a four-electron deficiency per unit cell, and such a derivative with Sc substituting for Mg is an appropriate quasicrystal approximant (Im3̄). Such characteristics seem to be key factors in the formation of icosahedral quasicrystals

Development of an Icosahedral Quasicrystal and Two Approximants in the Ca-Au-Sn System: Syntheses and Structural Analyses

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 Im3̅, a = 15.131(1) Å, whereas a representative 2/1 AC gives Ca13Au47.2(1)Sn28.1(1), Pa3̅ 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 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 states of Au and Sn

Ca4Au10In3: Synthesis, Structure, and Bonding Analysis. The Chemical and Electronic Transformations of the Isotypic Zr7Ni10 Intermetallic

The title compound, Ca4Au10In3 (e/a = 1.59), was synthesized by conventional high-temperature solid-state reactions and structurally analyzed by single-crystal X-ray diffraction:  space group Cmca, a = 13.729(4) Å, b = 10.050(3) Å, c = 10.160(3) Å, Z = 4. The structure, isotypic with that of Zr7Ni10, features a novel three-dimensional [Au10In3] polyanionic framework built from sinusoidal Au layers that are interconnected by significant Au−Au and Au−In interactions. A prominent electronic feature is the presence of a pseudogap and empty bonding states above the Fermi level according to LMTO calculations, reminiscent of the tunable electronic properties discovered for Mg2Zn11-type phases. The natures of the chemical and electronic redistributions from Zr7Ni10 to Ca4Au10In3 are considered. The Au backbone appears to be particularly important