scholarly journals The Experimental Value of f(220) for Copper

1984 ◽  
Vol 37 (6) ◽  
pp. 651 ◽  
Author(s):  
JK Mackenzie ◽  
A McL Mathieson
Keyword(s):  
Form Factor ◽  
Electron Diffraction ◽  
The Other ◽  
Critical Voltage ◽  
Diffraction Measurement ◽  
X Ray ◽  
A Value ◽  
Atomic Form Factor ◽  
Ray Methods ◽  
Electron Diffraction Measurement

The value of the atomic form factor, /(220), for copper has been determined in recent years by a variety of methods. All the dynamical methods agree on a value in the region of 16'70-16�75. These methods include two X-ray methods, one involving measurement of intensity profiles and the other of Pendellosung beats, and also an electron diffraction measurement using a critical voltage procedure. By contrast, two recent kinematical measurements using y rays both report a distinctly different value of about 16�45. One of these determinations has already been re-examined by the present authors and the iscrepancy removed by an appropriate extrapolation to zero extinction.

Identification of a growth defect in solid C60 by electron diffraction

1992 ◽  
Vol 7 (2) ◽  
pp. 335-340 ◽  
Author(s):  
D.E. Luzzi ◽  
J.E. Fischer ◽  
X.Q. Wang ◽  
D.A. Ricketts-Foot ◽  
A.R. McGhie ◽  
...  
Keyword(s):  
Form Factor ◽  
Electron Diffraction ◽  
Diffraction Analysis ◽  
Powder Diffraction ◽  
Diffuse Scattering ◽  
Growth Defect ◽  
Electron Diffraction Analysis ◽  
Spherical Shells ◽  
Planar Defects ◽  
X Ray

The origin of an anomalous sawtooth-shaped feature in x-ray powder diffraction of solid C60 is explained via electron diffraction analysis. Films sublimed on holey carbon crystallize with close-packed (111) planes parallel to the surface. Rods of diffuse scattering are found along the 〈111〉 axis normal to the surface but not along other 〈111〉 axes. Powder averaging of these rods, coupled with the x-ray form factor of spherical shells with 3.5 Å radius, accounts for the sawtooth feature. We attribute this phenomenon to planar defects parallel to close-packed layers, which form during the growth of solid C60 by sublimation. A possibly related consequence of the growth mode is the observation of strong macroscopic (111) preferred orientation in films sublimed on a variety of substrates.

scholarly journals Die Kristallstruktur des Cyano-Elpasoliths [N(CH3)4]2CsFe(CN)6 / The Crystal Structure of the Cyano Elpasolite [N(CH3)4]2CsFe(CN)6

1982 ◽  
Vol 37 (12) ◽  
pp. 1534-1539 ◽  
Author(s):  
D. Babel
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
The Other ◽  
Methyl Groups ◽  
Orientational Disorder ◽  
Space Group ◽  
X Ray ◽  
Ray Methods ◽  
The Ideal

The crystal structure of the cubic compound [N(CH3)4]2CsFe(CN)6 was determined by X-ray methods: a = 2527.4(6) pm, space group Fd3c, Z = 32, Rg = 0.028 (260 independent single crystal reflections). The resulting distances within the practically undistorted Fe (CN)63- - octahedron are Fe-C = 193.4(6) and C-N = 115.7(7) pm. Compared to the ideal elpasolite structure of space group Fm3m, Z = 4, the octahedra are rotated by 7.4° through their 3 axis. This is discussed as caused by steric requirements of the tetramethylammonium groups (N-C = 148.4(10) and 149.1(38) pm, resp.). Three quarters of them, of which also the hydrogen positions could be located, are well oriented. The remaining quarter shows orientational disorder to approach similar contact distances as the other N(CH3)4+ ion exhibits between the methyl groups and the nitrogen ends of the anions

The transformation of groutite (α-MnOOH) into pyrolusite (MnO2)

1964 ◽  
Vol 33 (266) ◽  
pp. 1024-1031 ◽  
Author(s):  
J. Lima-De-Faria ◽  
A. Lopes-Vieira
Keyword(s):  
Single Crystal ◽  
Crystal Surface ◽  
Close Packing ◽  
The Other ◽  
X Ray ◽  
Detailed Interpretation ◽  
Homogeneous Mechanism ◽  
Ray Methods

SummaryThe transformation of groutite (α-MnOOH) by heating has been studied at 300° C in air, by single-crystal and powder X-ray methods. At this temperature groutite transforms topotactically into pyrolusite (MnO2), the a, b, and c axes of groutite becoming respectively the a, b, and c axes of pyrolusite (in pyrolusite b = a). At various stages of the transformation other weak and diffuse spots were observed on X-ray oscillation photographs, which could not be ascribed to pyrolusite. Some of these extra spots fit well to an α-Mn2O3 structure (isostructural with hematite), with c 14·3 and a 4·9 Å; the other few spots could not be identified.The transformation of α-MnOOH into MnO2 is explained by a homogeneous mechanism, with migration of protons and electrons to the crystal surface. A detailed interpretation of this mechanism is presented on the basis of the close-packing characteristics of these two structures.

scholarly journals Inclusion of the insecticide fenitrothion in dimethylated-β-cyclodextrin: unusual guest disorder in the solid state and efficient retardation of the hydrolysis rate of the complexed guest in alkaline solution

2013 ◽  
Vol 9 ◽  
pp. 106-117 ◽  
Author(s):  
Dyanne L Cruickshank ◽  
Natalia M Rougier ◽  
Raquel V Vico ◽  
Susan A Bourne ◽  
Elba I Buján ◽  
...  
Keyword(s):  
Kinetic Studies ◽  
The Other ◽  
Hydrolysis Rate ◽  
Crystalline Inclusion ◽  
X Ray Diffraction ◽  
X Ray ◽  
A Value ◽  
Host Compound ◽  
Hydrolysis Of ◽  
Remarkable Reduction

An anhydrous 1:1 crystalline inclusion complex between the organophosphorus insecticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl)phosphorothioate] and the host compound heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) was prepared and its structure elucidated by single-crystal X-ray diffraction. This revealed two independent host molecules in the asymmetric unit. In one of these, the cavity is occupied by two disordered guest components (distinguishable as rotamers with respect to the P–OAr bond) while in the other, three distinct guest components with site-occupancies 0.44, 0.29 and 0.27 appear, the last having a reversed orientation relative to all the other components. Kinetic studies of the alkaline hydrolysis of fenitrothion in the presence of DIMEB showed a remarkable reduction of 84% in the rate of this reaction relative to that for the free substrate, a value exceeding those previously attained with the native hosts, β- and γ-cyclodextrin, and fully methylated β-cyclodextrin.

Absolute Präzisionsbestimmungen von Gitterkonstanten an Silicium-Einkristallen mit Elektroneninterferenzen *

1967 ◽  
Vol 22 (1) ◽  
pp. 79-91
Author(s):  
H. Kiendl
Keyword(s):  
Electron Diffraction ◽  
X Ray Diffraction ◽  
Present Measurement ◽  
X Ray ◽  
Lattice Constants ◽  
Solid Crystal ◽  
Accuracy Of Measurement ◽  
A New Technique ◽  
Relative Measurements ◽  
Ray Methods

Absolute precise determinations of lattice constants by electron diffraction, so far carried out for polycrystals with an accuracy of Δ a/a= ± 3 ·10-5 are now applied to thin single crystals. This precision is comparable with that of absolute X-ray methods. The factors determining the accuracy of measurement are discussed. — The lattice constants of thin silicon specimens, prepared by a new technique from a solid crystal, show none of the anomalies known from specimens prepared by vacuum evaporation and are in agreement with the value obtained by X-ray diffraction. These specimens therefore can be used as a standard for relative measurements of lattice constants. — The present measurement supports a new value of the conversion constant Λ between X-units and Angstrom units, which has been published (but not yet recommended) in 1965.

Interpenetrierende Clusterstränge in der Kristallstruktur von K0,77Nb6Cl15 / Interpenetrating Cluster Chains in the Structure of K0.77Nb6Cl15

2001 ◽  
Vol 56 (11) ◽  
pp. 1238-1240 ◽  
Author(s):  
Andreas Nägele ◽  
Cynthia Day ◽  
Abdessadek Lachgar ◽  
H.-Jürgen Meyer
Keyword(s):  
Solid State ◽  
Single Crystal ◽  
Solid State Reaction ◽  
Three Dimensional ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
A Value ◽  
Dimensional Network ◽  
Ray Methods

The solid state reaction of KCl, NbCl5 and Nb powder at 760 °C yielded black crystals of KNb6Cl15. The structure of the compound has been determined using single-crystal X-ray methods. KNb6Cl15 crystallizes in the orthorhombic space group Pmma (no. 51) with lattice constants a = 1780.1(2), b = 1341.4(1), and c = 925.5(1) pm, Z = 4, and R1 = 0.039 for all 2727 observed reflections.[(Nb6Cl12i)Cl6/2a-a]- anions in the structure are linked via two Cla-a bridges to form one set of linear and one set of kinked chains along the crystallographic c and a directions. Four remaining Cla-a bridges interconnect both sets of chains to a three-dimensional network. The potassium occupancy on a 4k site was refined to a value of 0.384(3) consistent with the formula K0.77Nb6Cl15-. Ternäre Niobchloride des Formeltyps ANb6Cl15 wurden bereits verschiedentlich beschrieben. Verbindungen mit A = Li [1] und Na [2] kristallisieren kubisch (Ia3̅d) mit identischen Schweratomstrukturen. Die Alkalimetall-Ionen Li (KZ = 4) und Na (KZ = 6 ) besetzen in den Strukturen ANb6Cl15 aber unterschiedliche Splitlagen und sind dynamisch fehlgeordnet. Die Vertreter mit A = In und TI [3] kristallisieren orthorhombisch (Pmma). Ihre Kationen befinden sich in zweifach überdachten, würfelförmigen Cl-Umgebungen (KZ = 10). Die Kenntnis des Formeltyps ANb6Cl15 mit schweren Alkalimetallen ist noch unvollständig. Einkristallstrukturuntersuchungen für A = Rb, Cs ergaben Kationenfehlordnungen [4, 5]. Für die Verbindung KNb6Cl15 wurde eine Einkristallstrukturbestimmung durchgeführt (Tab. 1). Die Verbindung kristallisiert orthorhombisch in der Raumgruppe Pmma (Nr. 51) mit den Gitterkonstanten a = 1780,1(2), b = 1341,4(1) und c = 925,5(1) pm mit Z = 4 und ist isotyp zu den Inund TI-Verbindungen. Die Besetzung der K-Position (4k-Lage, mx-Punktsymmetrie) wurde zu 0,384(3) verfeinert, was der Zusammensetzung K0.77Nb6Cl15 entspricht (Tab. 2)#. Die Nb-Nb-Abstände in KNb6Cl15 liegen zwischen 291,47(6) und 296,45(7) pm, die Bindungslängen Nb-ClI betragen 243,3(1) - 247,18(9) und die Nb-Cla-Abstände 258,7(2) - 271,40(9) pm.

Structural Phase Transition in Tetrafluoroaluminates

1982 ◽  
Vol 21 ◽  
Author(s):  
J.M. Launay ◽  
J.Y. Laval ◽  
A. Gibaud ◽  
A. Bulou ◽  
J. Nouet
Keyword(s):  
Electron Diffraction ◽  
Room Temperature ◽  
Structural Phase ◽  
The Other ◽  
Electron Diffraction Data ◽  
Temperature Phase ◽  
X Ray ◽  
Quadratic Phase ◽  
Low Temperature Phase ◽  
Good Agreement

ABSTRACTIt is shown that the detailed investigation of an irreversible SPT implies the combination of X-ray, neutron and electron diffraction data. This diffraction analysis is applied to K Al F4 and Rb Al F4. There is a good agreement between the three diffraction techniques in the case of Rb Al F4 where the SPT is reversible. On the other hand, for K Al F4 room temperature quadratic phase, electron diffraction exhibits exta spots which are not evidenced by X-ray and neutron diffraction. Finally the assumption of an orthorombic lattice from neutron scattering for the low temperature phase is consistant with electron diffraction results.

scholarly journals A Summary of Low-angle X-ray Atomic Scattering Factors Measured by the Critical Voltage Effect in High Energy Electron Diffraction

1988 ◽  
Vol 41 (3) ◽  
pp. 461 ◽  
Author(s):  
AG Fox ◽  
RM Fisher
Keyword(s):  
Electron Diffraction ◽  
Form Factors ◽  
High Energy ◽  
Energy Electron ◽  
Free Atom ◽  
Critical Voltage ◽  
High Energy Electron ◽  
X Ray ◽  
Hexagonal Close Packed ◽  
Atomic Scattering

A summary of all the accurate (-0.1%) low-angle X-ray atomic scattering (form) factors for cubic and hexagonal close-packed elements which have been determined by the critical voltage technique in high energy electron diffraction (HEED) is presented. For low atomic number elements (Z ~ 40) the low-angle form factors can be significantly different to best free atom values, and so the best band structure calculated and/or X-ray measured form factors consistent with the critical voltage measurements are also indicated. At intermediate atomic numbers (Z:::: 40-50) only the very low-angle form factors appear to be different to the best free atom values, and even then only by small amounts. For heavy elements (Z ~ 70) the best free atom form factors appear to agree very closely with the critical voltage measured values and so, in this case, critical voltage measurements allow accurate determinations of Debye-Waller factors.

Crystal Structure of Methyl[tetrakis(pyrazol-1-yl)borato-N,N']mercury(II)

1987 ◽  
Vol 40 (9) ◽  
pp. 1609 ◽  
Author(s):  
AJ Canty ◽  
BW Skelton ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
The Other ◽  
X Ray ◽  
Ray Methods

Crystals of methyl[tetrakis(pyrazol-l-yl)borato-N,N']mercury(II) [MeHg(B(pz)4}] are triclinic, Pi, a 12.73(2), b 8.88(1), c 8.10(1) �, α 109.80(8), β 99.16(9), γ 103.05(10)�, Z 2. The structure, determined by single-crystal X-ray methods (R 0.12 for 1598 'observed' reflections), has molecules of MeHg(B(pz)4} with two pz groups coordinated to mercury, giving planar but irregular coordination. The more strongly bound group has Hg-N 2.07(4) A with C-Hg-N 169(2)�, and the other group has Hg-N 2.65(4)� with C-Hg-N 112(1)�.

Sign in / Sign up

Export Citation Format

Share Document