Johntomaite, a new member of the bjarebyite group of barium phosphates: description and structure refinement

2000 ◽  
Vol 70 (1-2) ◽  
pp. 1-14 ◽  
Author(s):  
U. Kolitsch ◽  
A. Pring ◽  
E. R. T. Tiekink
Keyword(s):  
Structure Refinement

Quantitative structure determination of interfaces through Z-contrast imaging and electron energy loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 104-105
Author(s):  
S. J. Pennycook ◽  
P. D. Nellist ◽  
N. D. Browning ◽  
P. A. Langjahr ◽  
M. Rühle
Keyword(s):  
Grain Boundaries ◽  
Cuprate Superconductors ◽  
Structure Refinement ◽  
3D Structure ◽  
Real Space ◽  
Contrast Imaging ◽  
Coordination Polyhedra ◽  
Burgers Vector ◽  
Z Contrast ◽  
Contrast Image

The simultaneous use of Z-contrast imaging with parallel detection EELS in the STEM provides a powerful means for determining the atomic structure of grain boundaries. The incoherent Z-contrast image of the high atomic number columns can be directly inverted to their real space arrangement, without the use of preconceived structure models. Positions and intensities may be accurately quantified through a maximum entropy analysis. Light elements that are not visible in the Z-contrast image can be studied through EELS; their coordination polyhedra determined from the spectral fine structure. It even appears feasible to contemplate 3D structure refinement through multiple scattering calculations.The power of this approach is illustrated by the recent study of a series of SrTiC>3 bicrystals, which has provided significant insight into some of the basic issues of grain boundaries in ceramics. Figure 1 shows the structural units deduced from a set of 24°, 36° and 65° symmetric boundaries, and 24° and 45° asymmetric boundaries. It can be seen that apart from unit cells and fragments from the perfect crystal, only three units are needed to construct any arbitrary tilt boundary. For symmetric boundaries, only two units are required, each having the same Burgers, vector of a<100>. Both units are pentagons, on either the Sr or Ti sublattice, and both contain two columns of the other sublattice, imaging in positions too close for the atoms in each column to be coplanar. Each column was therefore assumed to be half full, with the pair forming a single zig-zag column. For asymmetric boundaries, crystal geometry requires two types of dislocations; the additional unit was found to have a Burgers’ vector of a<110>. Such a unit is a larger source of strain, and is especially important to the transport characteristics of cuprate superconductors. These zig-zag columns avoid the problem of like-ion repulsion; they have also been seen in TiO2 and YBa2Cu3O7-x and may be a general feature of ionic materials.

X-ray Structure Refinement and Vibrational Spectroscopy of Ca8Gd2 (PO4)6 O2

2013 ◽  
Vol 12 (10) ◽  
pp. 719-726
Author(s):  
R. Ayadi ◽  
Mohamed Boujelbene ◽  
T. Mhiri
Keyword(s):  
Solid State ◽  
General Formula ◽  
Vibrational Spectroscopy ◽  
Powder Diffraction ◽  
Infrared Spectra ◽  
Solid State Reaction ◽  
Structure Refinement ◽  
Unit Cell ◽  
Cell Group ◽  
X Ray

The present paper is interested in the study of compounds from the apatite family with the general formula Ca10 (PO4)6A2. It particularly brings to light the exploitation of the distinctive stereochemistries of two Ca positions in apatite. In fact, Gd-Bearing oxyapatiteCa8 Gd2 (PO4)6O2 has been synthesized by solid state reaction and characterized by X-ray powder diffraction. The site occupancies of substituents is0.3333 in Gd and 0.3333 for Ca in the Ca(1) position and 0. 5 for Gd in the Ca (2) position.  Besides, the observed frequencies in the Raman and infrared spectra were explained and discussed on the basis of unit-cell group analyses.

Iron in kornerupine; a57Fe Moessbauer spectroscopic study and comparison with single-crystal structure refinement

1999 ◽  
Vol 84 (4) ◽  
pp. 536-549 ◽  
Author(s):  
Edward S. Grew ◽  
Guenther J. Redhammer ◽  
Georg Amthauer ◽  
Mark A. Cooper ◽  
Frank C. Hawthorne ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Spectroscopic Study ◽  
Structure Refinement ◽  
Single Crystal Structure ◽  
Crystal Structure Refinement

Structure refinement and impedance analysis of Ba0.85Ca0.15Zr0.10Ti0.90O3 ceramics sintered in air and nitrogen

2019 ◽  
Vol 30 (23) ◽  
pp. 20673-20686
Author(s):  
Ku Noor Dhaniah Ku Muhsen ◽  
Rozana Aina Maulat Osman ◽  
Mohd Sobri Idris
Keyword(s):  
Structure Refinement ◽  
Impedance Analysis

scholarly journals Effect of Cd and SPD on structure, physical, mechanical, and operational properties of alloy of Cu-Cr-Zr

2020 ◽  
Vol 59 (1) ◽  
pp. 506-513
Author(s):  
Denis A. Aksenov ◽  
Georgiy I. Raab ◽  
Rashid N. Asfandiyarov ◽  
Vladimir I. Semenov ◽  
Lev Sh. Shuster
Keyword(s):  
Wear Resistance ◽  
Structure Refinement ◽  
Alloy System ◽  
Environmental Safety ◽  
Structural Refinement ◽  
Industrial Systems ◽  
Ultrafine Grained ◽  
Positive Effect ◽  
Complete Processing ◽  
Zr Alloy

AbstractAn increase in the service life of electrical products from copper and its alloys is directly related to an increase in the wear resistance of materials. Structural refinement and alloying with cadmium are known to have a positive effect on the strength characteristics and wear resistance of copper, which makes it possible, with a Cd content of 1% by weight, to increase the wear resistance of copper several times, but cadmium is considered an environmentally unsafe element. In this regard, the paper presents the results of studies of a widely used Cu-Cr-Zr alloy system in the ultrafine-grained (UFG) state, micro-alloyed with cadmium (0.2%, weight), in order to improve physical, mechanical, and operational properties, as well as environmental safety. Severe plastic deformation, providing structure refinement to ~150 nm, and microalloying with cadmium of a Cu-Cr-Zr system alloy, after a complete processing cycle, provides a tensile strength of 570±10 MPa and 67% electrical conductivity. At the same time, the abrasion resistance increases by 12 and 35% relative to the industrial systems Cu-Cd and Cu-Cr-Zr, respectively. The obtained characteristics are very promising for improving the operational properties of continuous welding tips, collector plates, and contact wires operating under conditions of intense wear.

Structure Investigations of Agonists of the Natural Neurotransmitter Acetylcholine, IV [1]. X-Ray Structure Analyses of Trimethylpentylammonium-chloride and (4-Acetoxybutyl) trimethylammonium-iodide

1986 ◽  
Vol 41 (5-6) ◽  
pp. 618-626
Author(s):  
Alfred Gieren ◽  
Michail Kokkinidis
Keyword(s):  
Structure Refinement ◽  
Pharmacological Action ◽  
Ammonium Nitrogen ◽  
Carbonyl Oxygen ◽  
Type B ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Structure Investigations ◽  
Automatic Diffractometer

The crystal structures of the title compounds which display cholinergic activity at the ganglionic receptor have been determined by X-ray structure analysis. [(CH3)3N+C5H11]Cl- (1) crystallizes in the orthorhombic space group Pbnm with half a formula unit per asymmetric unit, a = 11.381(14). b = 12.871(17), c = 7.316(4) Å. The intensities of 1106 independent reflections were collected with an automatic diffractometer. The structure refinement converged at R = 0.133 for the 355 observed reflections. The cation of 1 is disordered. [(CH3)3N + (CH2)4-O-C(O)-CH3]I- (2) crystallizes in the orthorhombic space group P212121 with four formula units per unit cell, a = 16.783(8), b = 10.276(6), c = 7.427(10) Å. The intensities of 1469 independent reflections were collected. The structure refinement converged at R = 0.071 for 1383 observed reflections. In both compounds the trimethylammonio methyl groups are coordinated nearly tetrahedrally by four anions in the first coordination sphere. Anions which occupy a special face type (B) of the tetrahedron of the (CH3)3N+ -CH2-group may be treated as a “model binding site” of the receptor. In the crystal structure of 2 the anions occupying B-type faces form together with the ammonium nitrogen and the carbonyl oxygen so called “Activity triangles”. The almost equal geometries of these activity triangles are correlated with the mode of pharmacological action.

scholarly journals Bulk and Confined Benzene-Cyclohexane Mixtures Studied by an Integrated Total Neutron Scattering and NMR Method

2021 ◽  
Author(s):  
Terri-Louise Hughes ◽  
Marta Falkowska ◽  
Markus Leutzsch ◽  
Andrew J. Sederman ◽  
Mick D. Mantle ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Structure Refinement ◽  
Computational Simulation ◽  
Liquid Mixtures ◽  
Coordination Shell ◽  
Bulk Liquid ◽  
Total Neutron ◽  
Time Resolved ◽  
Sample Composition ◽  
Potential Structure

AbstractHerein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement.

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