EXAFS study of intermetallics of the type RGe2 (R=La,Ce, Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Y) Part I: Determination of Ge-Ge distances

A study of theEXAFS associated with theK x-ray absorption discontinuity of germanium in pure germanium and in the rare-earth germanides RGe₂ (where R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) has been carried out. The Ge-Ge distances have been obtained in these compounds. Considering the phase to the RGe₂ system, the bond lengths in these compounds have been determined. The values obtained by us for the RGe₂ compounds (R=La, Ce, Pr, Nd, Sm, Gd, Dy and Y) agree with those obtained earlier by crystallographic methods. The bond lengths for the compounds TbGe₂, HoGe₂ and ErGe₂ are also being reported.     

Structure-Bonding Relationships in the Laves Phases

The Laves phase structures (MgCu₂ MgZn₂ and MgNi₂ types) are adopted by a large number of binary intermetallic compounds of composition AB₂. These phases belong to the class of tetrahedrally closepacked alloys. Two of the structural features of the Laves phases which have aroused interest are, firstly the dependence of the structure adopted (especially the choice between the cubic MgCu₂ and hexagonal MgZn₂ types) on the number of valence electrons of the constituent metal atoms and, secondly the structural distortions observed in a number of the hexagonal MgZn₂ type phases. By performing extended Hückel band calculations on model AB₂ compounds with both the cubic and hexagonal structures and on the B sub-nets alone, structure electron-count and deformation-electron count correlations are derived. These correlations depend on the highly peaked nature of the density of states of the Laves phases, primarily due to the B network.     

Yb5Ni4Sn10 and Yb7Ni4Sn13: New polar intermetallics with 3D framework structures

The title compounds have been obtained by solid state reactions of the corresponding pure elements at high temperature, and structurally characterized by single-crystal X-ray diffraction studies. Yb₅Ni₄Sn₁₀ adopts the Sc₅Co₄Si₁₀ structure type and crystallizes in the tetragonal space group P4/mbm (No. 127) with cell parameters of a=13.785(4) Å, c=4.492 (2) Å, V=853.7(5) Å³, and Z=2. Yb₇Ni₄Sn₁₃ is isostructural with Yb₇Co₄InGe₁₂ and crystallizes in the tetragonal space group P4/m (No. 83) with cell parameters of a=11.1429(6) Å, c=4.5318(4) Å, V=562.69(7) Å³, and Z=1. Both structures feature three-dimensional (3D) frameworks based on three different types of one-dimensional (1D) channels, which are occupied by the Yb atoms. Electronic structure calculations based on density functional theory (DFT) indicate that both compounds are metallic. These results are in agreement with those from temperature-dependent resistivity and magnetic susceptibility measurements.     

Synthesis, structure, and physical properties of Ce2PdGa10

A new ternary compound, Ce₂PdGa₁₀, has been synthesized using Ga flux and characterized by single-crystal X-ray diffraction. Ce₂PdGa₁₀ adopts a tetragonal structure in the I₄/mmm space group and is isostructural to Ce₂NiGa₁₀. Lattice parameters are , , , and Z=2. The compound is metallic (dρ/dT>0), with the resistance decreasing roughly linearly with temperature from 300 to 175 K. The magnetic susceptibility of Ce₂PdGa₁₀ is consistent with local-moment paramagnetism and no long-range magnetic ordering occurs down to 2 K. A large positive magnetoresistance over 200% is observed at 2 K for fields of 9 T. In this paper, we present the structure and physical properties of Ce₂PdGa₁₀ and compared them to CePdGa₆.     

Characteristics of CuAl<Subscript>2</Subscript>-Cu<Subscript>9</Subscript>Al<Subscript>4</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites synthesized by mechanical treatment

Summary Reactive milling of Cu-hydroxycarbonate - powder aluminium mixture brings many complex chemical reactions such as decomposition, aluminothermic reduction and mechanical alloying resulting in the formation of nanometer size composites that contain intermetallic phases, -Cu₉Al₄ and -CuAl₂, with aluminium oxide.     

Magnetic properties and electronic structure of GdNi4Si compound

Electronic structure of the ternary GdNi₄Si compound, crystallizing in hexagonal CaCu₅ structure (P6/mmm space group) was studied by magnetic measurements, X-ray photoelectron spectroscopy (XPS) and ab initio calculations. Core levels and valence band were investigated. The valence band of the XPS spectra is determined mainly by the Ni(3d) and Gd(4f) bands. The peaks’ positions are in good agreement with binding energies of a metallic gadolinium and nickel. The experimental valence band spectrum as well as the calculated density of states exhibit the domination of the Ni(3d) states in region from −4 eV to the Fermi level.     

Discovery of a Superconducting Cu–Bi Intermetallic Compound by High‐Pressure Synthesis

A new intermetallic compound, the first to be structurally identified in the Cu?Bi binary system, is reported. This compound is accessed by high‐pressure reaction of the elements. Its detailed characterization, physical property measurements, and ab initio calculations are described. The commensurate crystal structure of Cu₁₁Bi₇ is a unique variation of the NiAs structure type. Temperature‐dependent electrical resistivity and heat capacity measurements reveal a bulk superconducting transition at T_c=1.36 K. Density functional theory calculations further demonstrate that Cu₁₁Bi₇ can be stabilized (relative to decomposition into the elements) at high pressure and temperature. These results highlight the ability of high‐pressure syntheses to allow for inroads into heretofore‐undiscovered intermetallic systems for which no thermodynamically stable binaries are known.