X-ray powder diffraction and electron diffraction studies of the thortveitite-related L phase, (Zn,Mn)2V2O7

2009 ◽  
Vol 65 (2) ◽  
pp. 160-166 ◽  
Author(s):  
Kevin M. Knowles ◽  
Mary E. Vickers ◽  
Anjan Sil ◽  
Yung-Hoe Han ◽  
Périne Jaffrenou
Keyword(s):  
Electron Diffraction ◽  
Powder Diffraction ◽  
System Analysis ◽  
Bravais Lattice ◽  
Second Phase ◽  
X Rays ◽  
X Ray ◽  
The Difference ◽  
Diffraction Patterns ◽  
A Minor

The phase designated γ-Zn3(VO4)2 reported as a minor second phase in zinc oxide-based varistor materials doped with vanadium oxide and manganese oxide is shown to be the L phase, (Zn1 − x Mn x )2V2O7 (0.188 < x < 0.538), in the pseudo-binary Mn2V2O7–Zn2V2O7 system. Analysis of X-ray powder diffraction patterns and electron diffraction patterns of this phase shows that the previously published a, c and β values for this thortveitite-related phase are incorrect. Instead, Rietveld refinement of the X-ray powder pattern of the L phase shows that it has a monoclinic C lattice with Z = 6, with a  =  10.3791 (1), b = 8.5557 (1), c = 9.3539 (1) Å and β = 98.467 (1)°. Although prior convergent-beam electron diffraction work of `γ-Zn3(VO4)2' confirmed the C Bravais lattice, the space group was found to be Cm rather than C2/m, the difference perhaps arising from the inability of the X-rays to detect small displacements of oxygen. Attempts to refine the structure in Cm did not produce improved R factors. The relationship between the crystal structure of the L phase and the high-temperature C2/m β′-Zn2V2O7 thortveitite-type solid solution is discussed.

New Applications of Electron Diffraction in the Pharmaceutical Industry: Polymorph Determination by Using a Combination of Electron Diffraction and Synchrotron X-ray Powder Diffraction Techniques

2002 ◽  
Vol 8 (2) ◽  
pp. 134-138 ◽  
Author(s):  
Z.G. Li ◽  
R.L. Harlow ◽  
C.M. Foris ◽  
H. Li ◽  
P. Ma ◽  
...  
Keyword(s):  
Pharmaceutical Industry ◽  
Electron Diffraction ◽  
Powder Diffraction ◽  
Unit Cell ◽  
X Ray ◽  
Cell Parameters ◽  
Synchrotron Powder Diffraction ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
New Applications

Electron diffraction has been recently used in the pharmaceutical industry to study the polymorphism in crystalline drug substances. While conventional X-ray diffraction patterns could not be used to determine the cell parameters of two forms of the microcrystalline GP IIb/IIIa receptor antagonist roxifiban, a combination of electron single-crystal and synchrotron powder diffraction techniques were able to clearly distinguish the two polymorphs. The unit-cell parameters of the two polymorphs were ultimately determined using new software routines designed to take advantage of each technique's unique capabilities. The combined use of transmission electron microscopy (TEM) and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large-unit-cell, micron-sized) polymorphic pharmaceutical compounds.

Full-field energy-dispersive powder diffraction imaging using laboratory X-rays

2015 ◽  
Vol 48 (1) ◽  
pp. 269-272 ◽  
Author(s):  
Christopher K. Egan ◽  
Simon D. M. Jacques ◽  
Matthew D. Wilson ◽  
Matthew C. Veale ◽  
Paul Seller ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Texture Mapping ◽  
Friction Stir Weld ◽  
Field Energy ◽  
X Rays ◽  
Full Field ◽  
X Ray ◽  
Friction Stir ◽  
Diffraction Imaging ◽  
Diffraction Patterns

A laboratory instrument with the ability to spatially resolve energy-dispersed X-ray powder diffraction patterns taken in a single snapshot has been developed. The experimental arrangement is based on a pinhole camera coupled with a pixelated spectral X-ray detector. Collimation of the diffracted beam is defined by the area of the footprint of a detector pixel and the diameter of the pinhole aperture. Each pixel in the image, therefore, contains an energy-dispersed powder diffraction pattern. This new X-ray imaging technique enables spatial mapping of crystallinity, crystalline texture or crystalline phases from within a sample. Validation of the method has been carried out with a back-to-back comparison with crystalline texture mapping local to a friction stir weld in an aluminium alloy taken using synchrotron radiation.

scholarly journals Electron Diffraction vs aperiodic crystal: from indexation to structure solution

2014 ◽  
Vol 70 (a1) ◽  
pp. C1194-C1194
Author(s):  
Philippe Boullay ◽  
Gwladys Mouillard ◽  
Nicolas Barrier ◽  
Olivier Perez ◽  
Lukas Palatinus
Keyword(s):  
Electron Diffraction ◽  
Powder Diffraction ◽  
Structural Model ◽  
Neutron Powder Diffraction ◽  
Accurate Estimation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution ◽  
The Difference ◽  
Aperiodic Crystals

Can we solve aperiodic structures using intensities from electron diffraction? Yes! How? No mystery about it: the data analysis and the tools used for structure solution are essentially the same as the ones used in X-ray crystallography. The trick actually lies in new approaches used in electron crystallography. In analogy to X-ray diffraction, the so-called Electron Diffraction Tomography (EDT) [1] corresponds to a phi-scan data collection on a single crystal. There lies one major advantage of this technique: a powder sample is easily converted to infinitely large number of single crystals for electron diffraction. In case of aperiodic crystals this makes the difference over X-ray or neutron powder diffraction where, often, the lack of peaks clearly assignable to satellite reflections prevents any indexation and further analysis of the structure [2]. EDT allows for an accurate estimation of the modulation vector and a good guess of the super space group. These informations can be advantageously used as an input for X-ray or neutron powder diffraction. Not limited to indexation, EDT combined with Precession Electron Diffraction (PED) [3], offers a unique tool for solving modulated structures when crystals suitable for X-ray diffraction are missing. By limiting the paths for multiple scattering, PED makes the diffracted intensities closer to kinematical approximation so that they can be used efficiently for structure solution. Regarding aperiodic crystals, the superspace electron density map, generated as an output of the charge flipping algorithm used in Superflip, can be interpreted to obtain a structural model. This will be illustrated on a series of layered materials closely related to the Aurivillius phases belonging to the pseudo-binary Bi5Nb3O15-ABi2Nb2O9 (A=Pb, Sr, Ca, Ba). Limitations and possible combination with powder diffraction patterns will be discussed.

EDP2XRD: a computer program for converting electron diffraction patterns into X-ray diffraction patterns

2016 ◽  
Vol 49 (2) ◽  
pp. 636-641 ◽  
Author(s):  
Hongwei Liu ◽  
Matthew Foley ◽  
Qingyun Lin ◽  
Jiangwen Liu
Keyword(s):  
Electron Diffraction ◽  
Region Of Interest ◽  
Volume Ratio ◽  
Small Region ◽  
Homogeneous Distribution ◽  
X Ray Diffraction ◽  
Commercial Software ◽  
X Ray ◽  
The Difference ◽  
Diffraction Patterns

Mny commercial software packages for X-ray diffraction pattern analysis are capable of identifying multiple phases in bulk materials. However, X-ray diffraction patterns cannot record those phases with very small volume ratio or non-homogeneous distribution, which may mean that researchers have to use instead electron diffraction patterns from a very small region of interest. EDP2XRD, a new program for converting electron diffraction patterns into X-ray diffraction patterns, is described here. The program has been developed in order to utilize X-ray analysis software for electron diffraction patterns taken from mixed-phase nanocrystalline materials with a transmission electron microscope. It is specifically designed for material researchers who are engaged in crystallographic microstructure analysis. The difference from other popular commercial software for crystallography is that this program provides new options to convert and plot X-ray diffraction patterns for arbitrary electron diffraction rings and to process raw images to enhance conversion performance. The program contains the necessary crystallographic calculator to list planar d spacings and corresponding X-ray diffraction angles.

scholarly journals The diffraction of electrons by graphite

1936 ◽  
Vol 155 (885) ◽  
pp. 345-365 ◽  
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Graphite Powder ◽  
Current View ◽  
X Rays ◽  
X Ray ◽  
Artificial Graphite ◽  
Graphite Structure ◽  
Diffraction Patterns ◽  
Pass Through

The structure first attributed to graphite by Debye and Scherrer, and by Hull from X-ray powder patterns was confirmed by Hassell and Mark, by Bernal, and, finally, by Mauguin and Ott who relied mainly on single crystal X-ray photographs. The assigned structure is such that the hexagonal unit cell has the dimensions, a = 2·46 and c = 6·79 A, and contains two pairs of crystallographically different carbon atoms of coordinates (0, 0, 0), (0, 0, ½), (⅓, ⅔, u ), and (⅔, ⅓, u + ½), where, according to Ott, u < 0·004. Hence we may picture the graphite crystal as consisting of carbon atoms situated at the points of plane, or nearly plane hexagonal network sheets parallel to, and equidistant from, each other, and so superimposed that the projections from hexagon centres in one sheet pass through atoms in the two neighbouring sheets. Thus the atoms in alternate sheets are superimposed. Trendelenburg, Miwa, and Jenkins studied the diffraction of electrons by graphite powder and concluded that their results were in agreement with X-rays, apart from the absence or undue weakness of the 001 diffractions. This difference was satisfactorily explained by these workers as being due to the effect of the flake-like form of the crystals and the inner potential of graphite, the latter being known from measurements by Yamaguti and Jenkins of electron-diffraction patterns obtained by reflexion at single-crystal cleavage faces. A similar conclusion was reached by other workers who, however, have not published diffraction patterns in substantiation of their findings. Finally, Aminoff and Broome considered that the spot patterns and a Kikuchi line pat-tern obtained by them by transmission of electrons through relatively thin and thicker graphite flakes respectively were in general agreement with the accepted graphite structure, and indicated hexagonal symmetry of the structure with respect to the c axis or cleavage face normal. In the course of a study of the lubricating properties of graphite, we obtained transmission patterns of graphite films formed by the drying-out of a colloidal artificial graphite (“Aquadag”) solution. Although these patterns at first sight appeared to resemble those hitherto obtained by X-ray and electron diffraction, a closer inspection revealed the existence of several rings which had previously not been observed, doubtless because of insufficient resolution, and which did not appear to fit in with the current view of the structure of the graphite lattice. It is the object of this communication to set forth these differences and to elucidate their origin.

Sub-nanosecond X-ray powder diffraction

1990 ◽  
Vol 23 (5) ◽  
pp. 441-443 ◽  
Author(s):  
N. C. Woolsey ◽  
J. S. Wark ◽  
D. Riley
Keyword(s):  
Powder Diffraction ◽  
Laser Light ◽  
Polycrystalline Materials ◽  
Spectral Brightness ◽  
X Rays ◽  
Single Exposure ◽  
Time Resolved ◽  
X Ray ◽  
Titanium Target ◽  
Diffraction Patterns

The X-rays emitted from a laser-produced plasma have been used to obtain powder diffraction patterns with exposures of less than a nanosecond. The X-rays were produced by focusing approximately 50 J of 0.53 μm laser light in a 600 ps (FWHM) pulse to a tight (~100 μm diameter) spot on a solid titanium target. The spectral brightness of the resonance line of the helium-like titanium thus produced was sufficient to record diffraction from LiF powder in a single exposure using the Seemann–Bohlin geometry. These results indicate that time-resolved measurements of the lattice parameters of polycrystalline materials can be made with sub-nanosecond temporal resolution.

The Value of X-ray Powder Diffraction Patterns, and the Structure of the Manganese-Aluminum Alloys with Apparent Icosahedral Symmetry

1986 ◽  
Vol 1 (1) ◽  
pp. 14-15 ◽  
Author(s):  
Linus Pauling
Keyword(s):  
Powder Diffraction ◽  
Bragg Reflection ◽  
Icosahedral Symmetry ◽  
X Rays ◽  
X Ray ◽  
California Institute Of Technology ◽  
Tetragonal Crystal ◽  
Institute Of Technology ◽  
Diffraction Patterns ◽  
Angle Of Reflection

I have made use of X-ray powder diffraction patterns for over sixty years. In the summer of 1922, in anticipation of my becoming a graduate student in chemistry, I read the book “X-Rays and Crystal Structure,” by W. H. and W. L. Bragg. Then in September 1922 I arrived in Pasadena, and immediately began to learn how to determine the structure of a crystal by a study of the X-ray diffraction pattern from Roscoe Gilkey Dickinson, who was the first person to have received a Ph.D. degree from the California Institute of Technology (1920). The procedure in use in Pasadena started with the preparation of a photograph showing lines obtained by Bragg reflection from a developed face of a large crystal with monochromatic radiation, usually molybdenum K alpha and beta. Measurement of the angle of reflection gave a set of possible values for the length of the edges of the unit of structure, usually of a cubic, hexagonal, or tetragonal crystal, since the methods were not powerful enough to permit the evaluation of more than two or three parameters. The next step was the preparation of Laue photographs, and their analysis. This was a powerful method, which often led to the correct structures.

Powder Diffraction Pattern Simulation and Analysis

1993 ◽  
Vol 37 ◽  
pp. 101-107
Author(s):  
James K. Steele ◽  
Ronald R. Biederman
Keyword(s):  
Electron Diffraction ◽  
Powder Diffraction ◽  
Computer Code ◽  
Personal Computers ◽  
X Ray ◽  
The Past ◽  
Comparison Approach ◽  
Pattern Comparison ◽  
Diffraction Patterns ◽  
Pattern Simulation

The graphics capability and speed available in modern personal computers has encouraged an increase in the use of a direct pattern comparison approach to the analysis of x-ray and electron diffraction patterns. Several researchers over the past 30 years have presented programs and algorithms which calculate and display powder patterns for xray diffraction. These programs originally required a main frame computer which was expensive and generally not available to all researchers. With the recent advances in the speed of personal computers, language compilers, and high resoultion graphics, expecially within the past 5 years, real time calculations and display of calculated patterns is becoming widely available. The power of this approach will be demonstrated through the use of an IBM compatable personal computer code developed by the authors.

scholarly journals Modeling X-ray diffractomerers using ray tracing and parallel coprocessors

2014 ◽  
Vol 70 (a1) ◽  
pp. C1078-C1078
Author(s):  
Xim Bokhimi ◽  
Carlos Gonzalez
Keyword(s):  
Diffraction Pattern ◽  
Ray Tracing ◽  
Powder Diffraction ◽  
X Rays ◽  
Optical Components ◽  
X Ray ◽  
Crystalline Structures ◽  
Fundamental Parameters ◽  
Diffraction Patterns ◽  
Computer Facility

In X-ray powder diffraction, the use of the Rietveld technique to refine crystalline structures requires modeling the diffractometer. Some of the codes using this technique incorporate simple models for it. These codes do not affect the refined parameters only when the X-ray source is a synchrotron with enough X-ray optic to reduce the associated aberrations. When the diffractometer belongs to a standard laboratory, however, the optic associated to it gives rise to large aberrations; for example, asymmetric and shifted peaks that depend on the diffraction angle. When the above codes are used to refine crystalline structures, the refined parameters are non-confident, because they are partially modeling these aberrations. If in the code, the effect of the optical components on the diffraction pattern is modeled correctly, the obtained refined parameters will be more confident. This kind of modeling has been done in the codes that use the fundamental parameters model for the diffractometer. There are two ways to perform this modeling: in one of them the codes use an analytical model for each one of the optical components of the diffractometer; other codes use the ray tracing technique to model the path of the x-rays along the optic. This last technique requires a powerful computer facility. In this work, we present the developing of an open-source code to model the diffractometer by using the ray tracing technique. To reduce the calculation time, the code was written in OpenCL for a computer with a Fermi K20 coprocessor, and for a computer with a Xeon-Phi coprocessor, using the Qt platform for both systems. The device-function generated with this code can be used as input for any other code that models diffraction patterns, or refines crystalline structures. The code can also be used for teaching the effect of the different optical components on an X-ray powder diffraction pattern, including the effect of a wrong alignment of these components.

Structural studies of small amorphous volumes by electron diffraction

1990 ◽  
Vol 48 (4) ◽  
pp. 122-123
Author(s):  
Pierre Moine
Keyword(s):  
Electron Diffraction ◽  
Born Approximation ◽  
Structural Information ◽  
Fundamental Relation ◽  
X Rays ◽  
Structural Studies ◽  
Diffraction Experiment ◽  
Transmission Electron ◽  
Amorphous Structures ◽  
Diffraction Patterns

Qualitatively, amorphous structures can be easily revealed and differentiated from crystalline phases by their Transmission Electron Microscopy (TEM) images and their diffraction patterns (fig.1 and 2) but, for quantitative structural information, electron diffraction pattern intensity analyses are necessary. The parameters describing the structure of an amorphous specimen have been introduced in the context of scattering experiments which have been, so far, the most used techniques to obtain structural information in the form of statistical averages. When only small amorphous volumes (< 1/μm in size or thickness) are available, the much higher scattering of electrons (compared to neutrons or x rays) makes, despite its drawbacks, electron diffraction extremely valuable and often the only feasible technique.In a diffraction experiment, the intensity IN (Q) of a radiation, elastically scattered by N atoms of a sample, is measured and related to the atomic structure, using the fundamental relation (Born approximation) : IN(Q) = |FT[U(r)]|.

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