The crystal structure of eugaAl

1992 ◽  
Vol 50 (2) ◽  
pp. 1452-1453
Author(s):  
H. Brigitte Krause ◽  
Yonglin Qian
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
Zone Axis ◽  
Unit Cell ◽  
Polycrystalline Specimen ◽  
Lattice Constants

A polycrystalline specimen of nominal formula EuGaAl with unknown crystal structure was investigated by various electron microscope techniques; EDS-, SED-, and CBED data were taken on a Philips 400 electron microscope operated at 100kV, HREM data on a Hitachi 9000 microscope operated at 300kV. The EDS data confirmed the composition for the bulk of the material but, in addition, revealed particles with other fractions of the elements. Only the EuGaAl particles were further investigated. The unit cell was determined to be orthorhombic with a ratio: a/b=0.969(2) , a/c=0.234(2) and b/c=0.234(2). The lattice constants are a=4.54(5)Ȧ, b=4.68Ȧ and c=19.97(20)Ȧ. Based on systematic extinctions for hkl reflections with h+l=2n+l, the unit cell was found to be b-centered. CBED patterns of the [001], [100], and [010] zone axes are shown in Fig. 1. The zone axis patterns are in agreement with the above stated data except for diffused (2m+l,2n+l,0)- reflections, not compatible with the above stated systematic absences. But these occurred only occasionally in conjunction with a complicated noncommensurate superlattice pattern.

Anionische Komplexe [Mo2(O2CPh)4X2]2⊖ mit X = N3, Cl, Br. Die Kristallstruktur von (PPh4)2[Mo2(O2CPh)4Cl2] · 2CH2Cl2 / Anionic Complexes [Mo2(O2C-Ph)4X2]2⊖ with X = N3, Cl, Br. The Crystal Structure of (PPh4)2[Mo2(O2C-Ph)4Cl2] · 2CH2Cl2

1985 ◽  
Vol 40 (1) ◽  
pp. 13-18 ◽  
Author(s):  
Kay Jansen ◽  
Kurt Dehnicke ◽  
Dieter Fenske
Keyword(s):  
Crystal Structure ◽  
Ir Spectra ◽  
Diffraction Data ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
Anionic Complexes

The syntheses and IR spectra of the complexes [Mo2(O2C-Ph)4X2]2⊖ with X = N3, CI, Br and the counter ion PPh4⊕ are reported. The azido and the bromo complexes are obtained from a solution of [Mo2(O2CPh)4] with PPh4N3 in pyridine or by reaction with PPh4Br in CH2Br2, respectively. When (PPh4)2[Mo2(O2CPh)4(N3)2] is dissolved in CH2Cl2, nitrogen is evolved and the complex with X = CI is obtained. The crystal structure of (PPh4)2[Mo2(O2CPh)4Cl2] · 2CH2Cl2 was determined from X-ray diffraction data (5676 observed independent reflexions, R = 0.042). It crystallizes in the monoclinic space group P21/n with four formula units per unit cell; the lattice constants are a = 1549, b = 1400, c = 1648 pm, β = 94.6°. The centrosymmetric [Mo2(O2CPh)4Cl2]2⊖ ion has a rather short Mo-Mo bond of 213 pm, whereas the MoCl bonds are very long (288 pm)

Notizen: Eine neue bicyclische Zinn-Selen-Verbindung. Synthese und Kristallstruktur von [{Cp(CO)2Fe}3ClSn3Se4] / A New Bicyclic Tin Selenium Compound. Synthesis and Crystal Structure of [{Cp(CO)2Fe}3ClSn3Se4]

1993 ◽  
Vol 48 (7) ◽  
pp. 1009-1012 ◽  
Author(s):  
Kurt Merzweiler ◽  
Harald Kraus
Keyword(s):  
Crystal Structure ◽  
Structure Determination ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Synthesis And Crystal Structure ◽  
Selenium Compound ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
Compound Synthesis

[{Cp(CO)2Fe}SnCl3] reacts with Na2Se in THF to form the compound [{Cp(CO)2Fe}3ClSn3Se4] 1. 1 crystallizes in the monoclinic space group P21/n with 4 formula units per unit cell. The lattice constants are α = 1435.2(7), b = 1124.4(4), c = 1972.7(12) pm, β = 94.59(4)°. According to the X-ray structure determination 1 contains a bicyclic Sn3Se4 framework.

35Cl NQR, Crystal Structure, and C-Cl Bond Length of Cyclohexadienones

1988 ◽  
Vol 43 (10) ◽  
pp. 873-884 ◽  
Author(s):  
Stefanie Brummer
Keyword(s):  
Crystal Structure ◽  
Decomposition Temperature ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Lattice Constants ◽  
Group D ◽  
Cl Atoms

Abstract The 35Cl NQR spectra of 2,4,4,6-tetrachloro-3,5-dimethyl-cyclohexadiene-2,5-one-l and 2,4,4,6- tetrachloro-cyclohexadiene-2,5-one-l were studied from 77 K up to the decomposition temperature, their crystal structure having been determined by single crystal X-ray diffraction. The first com­pound crystallizes in the monoclinic space group C22h -P21/m with two molecules in the unit cell. The lattice constants are a = 887.2 (3) pm, b = 704.8 (3) pm, c = 824.0 (3) pm, β = 96.10(1)°. The sec­ond compound crystallizes orthorhombic, space group D182h - Cmca, with 8 molecules in the unit cell which has the dimensions a = 711.2(2) pm, b = 1388.4(3) pm, c = 1729.8(4) pm. The structures deter­mined belong to the stable phases of the title compounds as seen from the NQR spectra as a function of temperature which show no sign for a phase transition between the melting point and 77 K. In both title compounds the molecules are planar. Their symmetry is compared with other chloro- cyclohexadiene-2,5-ones-1 and chloro-cyclohexadiene-2,5-diones-1.4. The intramolecular distances d(C-Cl) of the sp2 carbon atoms and the 35Cl NQR frequencies assigned to the corresponding Cl atoms correlate quite well according to the theory: ν(35Cl) ~ (d(c-cl))-3 The relation is ν(35Cl)/MHz = 2 + 174 · 106 -(d/pm)-3.

Zur Struktur des Cycloheptatrienid-tricarbonyl-eisen(0)-Anions, [C7H7Fe(CO)3]– / The Structure of the Cyeloheptatrienide Triearbonyl Iron(O) Anion, [C7H7Fe(CO)3]-

1978 ◽  
Vol 33 (3) ◽  
pp. 261-264 ◽  
Author(s):  
Erich Sepp ◽  
Albert Pürzer ◽  
Gerhard Thiele ◽  
Helmut Behrens
Keyword(s):  
Crystal Structure ◽  
Ring System ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants

Abstract The crystal structure of the [C7H7Fe(CO)3]- anion stabilized with the [(C6H5)4As]+ cation has been determinated by X-ray diffraction. The crystals are monoclinic, space group P21/n. The unit cell with lattice constants a = 1607.9 pm, b = 1386.8 pm, c = 1249.1 pm and β - 91.52° includes four formula units. The Fe(CO)3 group is bonded to the allyl anion part of the C7H7 ring system, while the diene part is unco-ordinated.

P(C6H5)4[VOBr4]: Synthese, IR-Spektrum und Kristallstruktur / P(C6H5)4[VOBr4]: Synthesis, IR Spectrum and Crystal Structure

1982 ◽  
Vol 37 (6) ◽  
pp. 699-701 ◽  
Author(s):  
Ulrich Müller ◽  
Abdel-Fatah Shihada ◽  
Kurt Dehnicke
Keyword(s):  
Crystal Structure ◽  
Ir Spectrum ◽  
Structure Type ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
Dark Violet ◽  
Stretching Vibration

Abstract PPh4[VOBr4] was prepared by the reaction of PPh4Br with VOBr3 in CH2Br2 solu-tion. The structure of the dark violet crystals was determined with X-ray diffraction. PPh4[VOBr4] crystallizes in the space group P4/n with the lattice constants a = 1275.9 and c = 784.5 pm with two formula units per unit cell. The structure type corresponds to the frequently encountered AsPh4[RuNCl4] type. The VOBr4- ion forms a square pyramid; the V = O bond has a length of 155 pm. In the IR spectrum, the V -O stretching vibration appears at 922 cm-1 .

Notizen: Zur Reaktion von [(η3-C4H7)PdCl]2 mit Se(SiMe3)2 Die Kristallstruktur von [(η3-C4H7)6Pd6Se3] / Reaction of [(η3-C4H7)PdCl]2 with Se(SiMe3)2 The Crystal Structure of [(η3-C4H7)6Pd6Se3]

1988 ◽  
Vol 43 (5) ◽  
pp. 634-636 ◽  
Author(s):  
Dieter Fenske ◽  
Achim Hollnagel ◽  
Kurt Merzweiler
Keyword(s):  
Crystal Structure ◽  
Structure Analysis ◽  
Crystal Structure Analysis ◽  
Unit Cell ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
Trigonal Prismatic

[(η3-C4H7)PdCl]2 reacts with Se(SiMe3)2 to form [(η3-C4H7)6Pd6Se3] (1). 1 has been characterized by X-ray crystal structure analysis. It contains a distorted trigonal prismatic Pd6-cluster. Three faces of the Pd-prism are occupied by μ4-Se ligands. 1 crystallizes in the space group Pnma with 4 formula units per unit cell. The lattice constants at 200 K are: a = 1175.1(8), b = 1611.4(12), c = 1720.3(12) pm.

CHOICE OF Bi2223 UNIT CELL FOR TEXTURE STUDIES USING ORIENTATION DETERMINATION IN THE SCANNING ELECTRON MICROSCOPE

2005 ◽  
Vol 19 (07n08) ◽  
pp. 389-399
Author(s):  
D. LIN ◽  
W. LIU ◽  
A. GODFREY ◽  
Q. LIU
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Point Group ◽  
Unit Cell ◽  
Group Symmetry ◽  
Electron Backscatter ◽  
Unit Cells ◽  
Orientation Determination ◽  
Scanning Electron

Existing proposals for the crystal structure of the high temperature superconducting Bi 2 Sr 2 Ca 2 Cu 3 O 7-x ( Bi 2223) phase have been reviewed. For the purpose of automated orientation determination in the scanning electron microscope using electron backscatter pattern (EBSP) analysis, a new crystal structure is proposed, where the unit cell is assumed to be tetragonal with P4/mmm point-group symmetry. Simulated EBSP images corresponding to the various unit cells exhibit significant differences, confirming the importance of choosing the correct unit-cell information. The suitability of various choices of the unit cell for automated orientation determination using EBSP analysis has been investigated using experimental data. The newly proposed unit cell is superior to the other unit cells for each of the criteria used to assess the indexing ability.

CRYSTAL STRUCTURE AND SUPERCONDUCTIVITY OF Bi2Sr2CaCu2O8 COMPOUND

1988 ◽  
Vol 02 (01) ◽  
pp. 483-489 ◽  
Author(s):  
J.K. LIANG ◽  
S.S. XIE ◽  
G.C. CHE ◽  
J.Q. HUANG ◽  
Y.L. ZHANG ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Diffraction Method ◽  
Basic Structure ◽  
Unit Cell ◽  
Tetragonal Symmetry ◽  
Superconducting Transition ◽  
Lattice Constants ◽  
Point Position ◽  
Equivalent Point ◽  
The Ideal

The crystal structure of the ideal compositional compound Bi2Sr2CaCu2O8 with superconducting transition temperature Tc(0)=81.4K has been determined by X-ray powder diffraction method. The basic structure of this compound has the tetragonal symmetry with the lattice constants a=3.825Å, c=30.82Å. The most possible space group is [Formula: see text]. Each unit cell contains two chemical formulae. The arrangements of atoms in the unit cell are as follows: 2Ca cations occupy 2(a) equivalent point position 4Sr, 4Bi and 4Cu cations occupy the same equivalent point position 4(e) with respective parameters z=0.1, 0.3, 0.45. 16O anions respectively occupy 8(g) (z=0.45) and two 4(e) equivalent point positions (z=0.2 and z=0.385). The crystal structure of Bi2Sr2CaCu2O8 can be derived from Aurivillius type structure. The other possible superconducting phases in the Bi-Sr-Ca-Cu-O system can be considered as the structure having different stacking on the basis of Aurivillius phase.

Crystallographic Characterization of Dislocation Loops in Irradiated Tungsten

1968 ◽  
Vol 26 ◽  
pp. 290-291
Author(s):  
Robert C. Rau
Keyword(s):  
Electron Microscope ◽  
Ambient Temperature ◽  
Dislocation Loops ◽  
Polycrystalline Specimen ◽  
Post Irradiation ◽  
Neutron Fluences

Previous work has shown that post-irradiation annealing, at temperatures near 1100°C, produces resolvable dislocation loops in tungsten irradiated to fast (E > 1 MeV) neutron fluences of about 4 x 1019 n/cm2 or greater. To crystallographically characterize these loops, tilting experiments were carried out in the electron microscope on a polycrystalline specimen which had been irradiated to 1.5 × 1021 n/cm2 at reactor ambient temperature (∼ 70°C), and subseouently annealed for 315 hours at 1100°C. This treatment produced large loops averaging 1000 Å in diameter, as shown in the micrographs of Fig. 1. The orientation of this grain was near (001), and tilting was carried out about axes near [100], [10] and [110].

Toward quantitative defect analysis using HREM

1994 ◽  
Vol 52 ◽  
pp. 714-715
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscope ◽  
Unit Cell ◽  
Defect Analysis ◽  
Significant Progress ◽  
Detailed Characterization ◽  
Small Unit ◽  
Resolution Electron ◽  
High Resolution Electron Microscope ◽  
Large Unit Cell ◽  
Made In

The electron microscope has evolved to the level where it is now straightforward to record highresolution images from thin samples (t∼10 to 20nm) that are directly interpretable in terms of atomic arrangements. Whilst recorded images necessarily represent two-dimensional projections of the structure, many defects such as dislocations and interfaces may be linear or planar in nature and thus might be expected to be amenable to detailed characterization. In this review, we briefly consider the recent significant progress that has been made in quantitative defect analysis using the high-resolution electron microscope and then discuss some drawbacks to the technique as well as potential scope for further improvements. Surveys of defect modelling for some small-unit-cell materials and interfaces have recently been published, and reference should be made to other papers in this symposium for further examples.The technique of structure imaging originated in the early '70s with observations of large-unit-cell block oxides.

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