Sökresultat

Filtyp

Din sökning på "*" gav 534202 sökträffar

Comparative structural study of the disordered MCd6 quasicrystal approximants

Several of the MCd6 approximants (M=Pr, Nd, Sm, Eu, Gd, Dy, Yb, Y, and Ca) to the MCd5.7 quasicrystals (M=Yb and Ca) have been synthesized and their structures have been refined from single-crystal x-ray-diffraction data; the different types of disorder of the central Cd4 tetrahedra located in the dodecahedral cavities of these closely related compounds have been examined and mutually compared. A

New strontium and rare earth-based mixed niobium misfit sulfides

New niobium-based misfit sulfides (Ln1/3Sr2/3S)1.5]1.15 NbS2 (Ln = Sm, Tb) have been synthesized from a mixture of SrS, Ln2S3, Nb(m), and S in evacuated and sealed silica tubes by annealing at 1000 °C for 144 h under a sulfur partial pressure of 49.3 kPa. The compounds have been characterized by EDX analysis, X-ray single crystal and powder diffraction, electron diffraction, and magnetic susceptib

Order and twining in Sb2W0.75Mo0.25O6

Synthesis, X-rays, TEM and HREM studies of the composition x = 0.25 of the solid solution Sb2W1-xMoxO6 are reported. The phase crystallises in the monoclinic system, space group C2 and the cell parameters of its average structure are a = 11.1296(6) Å, b = 9.8868(9) Å, a = 18.501(2) Å, and β = 96.951(9)°. Mo and W atoms are ordered in the 1/3 ratio. Twining and extended defects have been studied by

Long-range ordering during delithiation of LiMn2O4 cathode material

A single crystal of the cubic spinel LiMn2O4 was delithiated electrochemically at 4.06 V vs. Li/Li+ to probe the structural source of the inflection point at ca. 4.1 V vs. Li/Li+ in the discharge curve. The phase thus obtained was investigated by single-crystal X-ray diffraction and the structure refined. The structure is closely related to the original cubic structure, but the new space group is

A general structure model for Bi-Se phases using a superspace formalism

Solid-state synthesis in the Bi-Se system produced both commensurate and incommensurate phases of compositions ranging from Bi2Se3 to Bi4Se3, all crystallising in rhombohedral or trigonal layer structures. The a parameters are very similar for all phases but the c parameters vary irregularly between 10 and 100 Å. A general model for all these phases was developed, using single crystal X-ray diffra

Synthesis of structurally controlled nanocarbons - In particular the nanobarrel carbon

Nanoporous carbons have been prepared through a selective etching reaction, performed by halogenisation of aluminum carbide. The structures obtained can be controlled by varying the chlorination temperature. The unique set of nanocarbons obtained include nanoporous amorphous structures, the nanobarrel structure and a nanographitic structure as chlorination temperatures were increased from 400 °C t

Effects from hydrogen bonds on water structure in (H3O)2[Mo6 Cl8X6]·yH2O X = Cl (y = 7), Br (y = 6), or I (y = 6)

The compounds (a) (H3O)2[Mo6Cl8 Cl6]·7H2O, (b) (H3O)2[Mo6 Cl8Br6]·6H2O and (c) (H3O)2[Mo6 Cl8I6].6H2O were synthesized from MoCl2 and the corresponding halide acid. The structures were determined by X-ray diffraction and refined in the monoclinic space groups, (a) C2/c and for (b) and (c) P21/a. The cell parameters were for (a), a = 17.3607(2), b = 9.1351(7), c = 18.6300(2) Å and β = 98.13(1)°, (b

Preparation and double-helix icosahedra structure of δ-Co2Zn15

The first known example of a regular face-sharing icosahedra helix is presented in the novel crystal structure of δCo2Zn15, solved and refined from single-crystal X-ray and neutron powder diffraction data. The compound δCo2Zn15 is also the first example of an intermetallic compound crystallizing in the acentric hexagonal space group P62. The parameters from the single crystal refinement are a = 11

Structure of Dy13Zn57 a binary quasicrystal approximant

The title compound Dy13Zn57, crystallizes in the orthorhombic space group Pnma (No. 62) with the cell parameters a = 14.060(5), b = 14.260(5) and c = 24.700(3) Å. The structure has formerly been described as Dy13Zn58 with the hexagonal type structure of Gd13Zn58. Single-crystal X-ray diffraction measurements however, show extra reflections breaking the C-centering of the corresponding orthorhombic

The structure of Nb5O12F

The title compound was synthesized according to Andersson Acta Chem. Scand. 18 (1964) 2233. The structure is an incommensurately modulated variation of the UO3 structure, in a (3 + 1)-dimensional super space description isostructural to the composite phases (1 - x)Ta2O5•xWO3 Acta Crystallogr., Sect. B 52 (1996) 223 and Acta Crystallogr., Sect. B 51 (1995) 709. The compound crystallizes in the orth

Superlattice formation in the lithiated vanadium oxide phases Li0.67V6O13 and LiV6O13

Two new lithiated phases of V6O13 were formed by carefully tuning the temperature of electrochemical lithiation in a 'coffee-bag' type Li-ion battery at 2.78 V versus Li/Li+. These were studied by single-crystal X-ray diffraction. A phase with the composition Li2/3V6O13 was obtained at 308 K with a unit cell three times the volume of the original V6O13 cell. A single crystal discharged at ambient

Anomalous vibrational dynamics in the Mg2Zn11 phase

We present a combined experimental and theoretical study of the structure and the lattice dynamics in the complex metallic alloy Mg2Zn 11, by means of neutron and x-ray scattering, as well as ab initio and empirical potential calculations. Mg2Zn11 can be seen as an intermediate step in structural complexity between the simple Laves-phase MgZn2 on one side, and the complex 1/1 approximants and quas

Structure of Ca13Cd76 : A novel approximant to the MCd5.7 Quasicrystals (M = Ca, Yb)

The closest cubic approximant to the MCd5.7 (M = Ca, Yb) quasicrystals known so far, namely Ca13Cd76, was obtained by high-temperature reaction of the elements. It exhibits a new type of structure for intermetallic compounds with an unprecedented arrangement of triacontahedral clusters (see structure), which could prove useful in modeling the structures of the MCd5.7 quasicrystals.

Incommensurately modulated Nowotny chimney-ladder phases : Cr1-xMoxGe∼1.75 with x = 0.65 and 0.84

The crystal structures of two new ternary, incommensurately modulated phases in the Cr/Mo/Ge system, Cr1-xMoxGe∼1.75 with x = 0.65 and 0.84, have been refined using the same composite approach as for the earlier reported compounds, (Mo/Rh)11Ge18 and (Mo/Rh)13Ge22, from the Mo/Rh/Ge system. The composite model consists of a rather stable diamond-like transition metal substructure and a helical main

Computer modeling and description of nonstoichiometric apatites Cd5-η/2(VO4)3I1-η and Cd5-η/2(PO4)3Br1-η as modified chimney-ladder structures with ladder-ladder and chimney-ladder coupling

Diffraction patterns from apatite-structure compounds Cd5-η/2(TO4)3X1-η with T=P, V and X=Br, I show sheets of diffuse scattering normal to c* at incommensurate l=q (q=1.63 for Cd-V-I apatite and q=1.78 for Cd-P-Br apatite), because the c repeat of the average unit cell is shorter than two X diameters. The equilibrium X..X spacing along c defines the incommensurate periodicity c/q and stoichiometr

Gallium and indium under high pressure

A study was carried out to explore the structural competition between the high symmetry fcc and low symmetry bct structure for the IIIA metals Al, Ga, and In. It was found that the competition originates from electronic properties. As a result, the high pressure behavior of the metals appears reversed to the corresponding-states rule.

Single crystsl refinement of the incommensurately modulated Mn0.55Ta0.45O1.7, an oxygen deficient fluorite type compound

A structural investigation of the incommensurately ordered compound Mn0.55Ta0.45O1.7 has been carried out, using single-crystal X-ray diffraction data. The basic structure is related to the fluorite type with a monoclinic distortion. Electron diffraction (ED) patterns for various crystal orientations were used for determination of unit cell, incommensurate modulation vector and superspace group. T

Reassessing the compound CeCd6 : the structure of Ce6Cd37

The crystal structure of the phase Ce6Cd37 was determined by single-crystal X-ray diffraction. It is closely related to, and indeed probably identical to, the previously reported compound CeCd6. The compound crystallizes in the centrosymmetric space group Pn3̄ with the unit cell axis 15.808(2) angstrom. The structure may be described by successive shells centered around the origin and the position