Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging-plate diffractometer

2017 ◽  
Vol 73 (4) ◽  
pp. 521-530 ◽  
Author(s):  
Kasper Tolborg ◽  
Mads R. V. Jørgensen ◽  
Sebastian Christensen ◽  
Hidetaka Kasai ◽  
Jacob Becker ◽  
...  
Keyword(s):  
Electron Density ◽  
High Energy ◽  
Imaging Plate ◽  
High Symmetry ◽  
X Rays ◽  
X Ray Diffraction ◽  
Core Electron ◽  
X Ray ◽  
Peak Broadening ◽  
Structure Factors

In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the sample-to-detector distance increased by a factor of four. In practice this is found to give a reduction in instrumental peak broadening by approximately a factor of three and a large improvement in signal-to-background ratio compared to the previous instrument. Structure factors of silicon at room temperature are extracted using a combined multipole–Rietveld procedure and compared withab initiocalculations and the results from the previous diffractometer. Despite some remaining issues regarding peak asymmetry, the new diffractometer yields structure factors of comparable accuracy to the previous diffractometer at low angles and improved accuracy at high angles. The high quality of the structure factors is further assessed by modelling of core electron deformation with results in good agreement with previous investigations.

Multipole electron densities and atomic displacement parameters in urea from accurate powder X-ray diffraction

2019 ◽  
Vol 75 (4) ◽  
pp. 600-609 ◽  
Author(s):  
Bjarke Svane ◽  
Kasper Tolborg ◽  
Lasse Rabøl Jørgensen ◽  
Martin Roelsgaard ◽  
Mads Ry Vogel Jørgensen ◽  
...  
Keyword(s):  
Electron Density ◽  
Molecular System ◽  
Atomic Displacement ◽  
High Symmetry ◽  
X Ray Diffraction ◽  
High Quality ◽  
Acta Cryst ◽  
X Ray ◽  
Density Determination ◽  
Structure Factors

Electron density determination based on structure factors obtained through powder X-ray diffraction has so far been limited to high-symmetry inorganic solids. This limit is challenged by determining high-quality structure factors for crystalline urea using a bespoke vacuum diffractometer with imaging plates. This allows the collection of data of sufficient quality to model the electron density of a molecular system using the multipole method. The structure factors, refined parameters as well as chemical bonding features are compared with results from the high-quality synchrotron single-crystal study by Birkedalet al.[Acta Cryst.(2004), A60, 371–381] demonstrating that powder X-ray diffraction potentially provides a viable alternative for electron density determination in simple molecular crystals where high-quality single crystals are not available.

A high-energy triple-axis X-ray diffractometer for the study of the structure of bulk crystals

2004 ◽  
Vol 37 (6) ◽  
pp. 901-910 ◽  
Author(s):  
C. Seitz ◽  
M. Weisser ◽  
M. Gomm ◽  
R. Hock ◽  
A. Magerl
Keyword(s):  
High Energy ◽  
X Rays ◽  
Bulk Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Peak Intensity ◽  
High Penetration ◽  
Massive Sample ◽  
Laue Geometry ◽  
The Ideal

A triple-axis diffractometer for high-energy X-ray diffraction is described. A 450 kV/4.5 kW stationary tungsten X-ray tube serves as the X-ray source. Normally, 220 reflections of thermally annealed Czochralski Si are employed for the monochromator and analyser. Their integrated reflectivity is about ten times higher than the ideal crystal value. With the same material as the sample, and working with the WKα line at 60 keV in symmetric Laue geometry for all axes, the full width at half-maximum (FWHM) values for the longitudinal and transversal resolution are 2.5 × 10−3and 1.1 × 10−4for ΔQ/Q, respectively, and the peak intensity for a non-dispersive setting is 3000 counts s−1. In particular, for a double-axis mode, an energy well above 100 keV from theBremsstrahlungspectrum can be used readily. High-energy X-rays are distinguished by a high penetration power and materials of several centimetre thickness can be analysed. The feasibility of performing experiments with massive sample environments is demonstrated.

Comparative study of X-ray charge-density data on CoSb3

2013 ◽  
Vol 69 (6) ◽  
pp. 570-582 ◽  
Author(s):  
Mette Stokkebro Schmøkel ◽  
Lasse Bjerg ◽  
Finn Krebs Larsen ◽  
Jacob Overgaard ◽  
Simone Cenedese ◽  
...  
Keyword(s):  
Charge Density ◽  
High Performance ◽  
Theoretical Data ◽  
High Energy ◽  
Data Sets ◽  
High Symmetry ◽  
X Ray ◽  
Structure Factors ◽  
Small Crystals ◽  
Density Analysis

CoSb3is an example of a highly challenging case for experimental charge-density analysis due to the heavy elements (suitability factor of ∼0.01), the perfect crystallinity and the high symmetry of the compound. It is part of a family of host–guest structures that are potential candidates for use as high-performance thermoelectric materials. Obtaining and analysing accurate charge densities of the undoped host structure potentially can improve the understanding of the thermoelectric properties of this family of materials. In a previous study, analysis of the electron density gave a picture of covalent Co–Sb and Sb–Sb interactions together with relatively low atomic charges based on state-of-the-art experimental and theoretical data. In the current study, several experimental X-ray diffraction data sets collected on the empty CoSb3framework are compared in order to probe the experimental requirements for obtaining data of high enough quality for charge-density analysis even in the case of very unsuitable crystals. Furthermore, the quality of the experimental structure factors is tested by comparison with theoretical structure factors obtained from periodic DFT calculations. The results clearly show that, in the current study, the data collected on high-intensity, high-energy synchrotron sources and very small crystals are superior to data collected at conventional sources, and in fact necessary for a meaningful charge-density study, primarily due to greatly diminished effects of extinction and absorption which are difficult to correct for with sufficient accuracy.

In situ time-resolved X-ray diffraction of tobermorite formation process under hydrothermal condition: Influence of reactive al compound

2011 ◽  
Vol 26 (2) ◽  
pp. 134-137 ◽  
Author(s):  
K. Matsui ◽  
A. Ogawa ◽  
J. Kikuma ◽  
M. Tsunashima ◽  
T. Ishikawa ◽  
...  
Keyword(s):  
Hydrothermal Reaction ◽  
High Energy ◽  
Saturated Steam ◽  
Array Detector ◽  
Time Interval ◽  
X Rays ◽  
X Ray Diffraction ◽  
Formation Reaction ◽  
X Ray

Hydrothermal formation reaction of tobermorite in the autoclaved aerated concrete (AAC) process has been investigated by in situ X-ray diffraction. High-energy X-rays from a synchrotron radiation source in combination with a newly developed autoclave cell and a photon-counting pixel array detector were used. XRD measurements were conducted in a temperature range 100–190°C throughout 12 h of reaction time with a time interval of 4.25 min under a saturated steam pressure. To clarify the tobermorite formation mechanism in the AAC process, the effect of Al addition on the tobermorite formation reaction was studied. As intermediate phases, non-crystalline calcium silicate hydrate (C-S-H), hydroxylellestadite (HE), and katoite (KA) were clearly observed. Consequently, it was confirmed that there were two reaction pathways via C-S-H and KA in the tobermorite formation reaction of Al containing system. In addition, detailed information on the structural changes during the hydrothermal reaction was obtained.

IN SITU STUDIES OF EPITAXIAL GROWTH BY SYNCHROTRON X-RAY DIFFRACTION

2006 ◽  
Vol 13 (02n03) ◽  
pp. 155-166 ◽  
Author(s):  
WOLFGANG BRAUN ◽  
KLAUS H. PLOOG
Keyword(s):  
Ostwald Ripening ◽  
Crystal Surface ◽  
High Energy ◽  
Molecular Beam Epitaxy Growth ◽  
X Rays ◽  
Surface Kinetics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Kinetics Of

X-rays are ideal to study the structure of crystals due to their weak interaction with matter and in most cases allow a quantitative analysis using kinematical theory. To study the incorporation of atoms during crystal growth and to analyze the kinetics on the crystal surface high primary beam intensities available at synchrotrons are required. Our studies of the molecular beam epitaxy growth of III–V semiconductors reveal that, despite their similarity in crystal structure, the surface kinetics of GaAs (001), InAs (001) and GaSb (001) differ strongly. GaAs shows an unexpectedly large coarsening exponent outside the predicted range of Ostwald ripening models during recovery. GaSb exhibits dramatically different surface morphology variations during growth and recovery. Overgrowth of GaAs by epitaxial MnAs demonstrates the ability of X-ray diffraction to follow an interface as it is buried during heteroepitaxy, which is not possible by reflection high-energy electron diffraction.

Recrystallization of AA1050 Studied by 3DXRD

2006 ◽  
Vol 519-521 ◽  
pp. 1569-1578
Author(s):  
Dorte Juul Jensen
Keyword(s):  
Single Crystals ◽  
High Energy ◽  
Nucleation And Growth ◽  
X Rays ◽  
X Ray Diffraction ◽  
Orientation Relationships ◽  
X Ray ◽  
3 Dimensional ◽  
Kinetics Of

By 3 dimensional X-ray diffraction (3DXRD) using high energy X-rays from synchrotron sources it is possible to study in-situ the nucleation and growth during recrystallization. In this paper it is described and discussed how 3DXRD can supplement EBSP measurements of nucleation and growth. Three types of studies are considered: i) orientation relationships between nuclei and parent deformed matrix, ii) recrystallization kinetics of individual bulk grains and iii) filming of growing grains in deformed single crystals.

Structure of Zr-Cu and Zr-Ni Liquid Alloys Studied by High-Energy X-Ray Diffraction

2007 ◽  
Vol 561-565 ◽  
pp. 1349-1352 ◽  
Author(s):  
Akitoshi Mizuno ◽  
T. Kaneko ◽  
Seiichi Matsumura ◽  
Masahito Watanabe ◽  
Shinji Kohara ◽  
...  
Keyword(s):  
Liquid Structure ◽  
High Energy ◽  
Glass Forming Ability ◽  
Liquid Alloys ◽  
X Ray Diffraction ◽  
X Ray ◽  
Glass Forming ◽  
Structure Factors ◽  
Asymmetric Shape ◽  
Second Peak

In order to obtain an insight into the high glass-forming ability of bulk metallic glasses, we have analyzed liquid structures of the Zr-Cu and the Zr-Ni binary alloys with different compositions. High-energy (E = 113 keV) x-ray diffraction experiments were carried out for the liquid alloys levitated by a conical nozzle levitation (CNL) technique. While a peculiar shoulder on the second peak was observed in the structure factors of the Zr-Cu liquid alloys, those of the Zr70Ni30 and the Zr50Ni50 liquids exhibit an asymmetric shape of the second peak. In addition, it was found that the effect of concentration variation in the liquid Zr-Ni alloys was significantly different from that of the liquid Zr-Cu alloys. The liquid structure analyses using the reverse Monte Carlo (RMC) simulation have clarified that a degree of the short-range correlation between the constituents in the liquids affects substantially the glass-forming ability of the binary Zr alloys.

Impact of Sn ions on structural and electrical description of TiO2 nanoparticles

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Mutaz Salih ◽  
M. Khairy ◽  
Babiker Abdulkhair ◽  
M. G. Ghoniem ◽  
Nagwa Ibrahim ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Simple Procedure ◽  
High Energy ◽  
X Rays ◽  
X Ray Diffraction ◽  
Energy Storage Devices ◽  
X Ray ◽  
Storage Devices ◽  
Transmission Electron ◽  
High Energy Storage

Abstract In this paper, Sn-doped TiO2 nanomaterials with varying concentrations were manufactured through a simple procedure. The fabricated TiO2 and Sn loaded on TiO2 nanoparticles were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-rays, Fourier transform infrared spectroscopy, and resistance analyses. The benefits of dielectric constant and ac conductivity rise at high Sn loaded concentration on TiO2 nanoparticles. The enhanced electrical conductivity is seen for STO3 (3.5% Sn doped TiO2) and STO4 (5% Sn doped TiO2) specimens are apparently associated with the introduced high defect TiO2 lattice. Furthermore, the fabricated specimens’ obtained findings may be applied as possible candidates for high-energy storage devices. Moreover, proper for the manufacture of materials working at a higher frequency.

X-Ray Diffraction as a Probe for Elastic Strain: Micro- and Nanoscale Investigation of Thin Metal Films

2004 ◽  
Vol 840 ◽  
Author(s):  
R. Spolenak
Keyword(s):  
Local Strain ◽  
Metal Films ◽  
X Rays ◽  
X Ray Diffraction ◽  
Large Area ◽  
Strain Measurements ◽  
X Ray ◽  
The Past ◽  
Time Space ◽  
Peak Broadening

ABSTRACTIn the past years the concept of measuring strain by x-rays has changed significantly. The combination of 3rd generation synchrotron sources, advanced focusing techniques and large area detectors has made it possible to probe volumes smaller than a cubic micron. This devolopment has made it possible to probe microstrains directly without having to rely on highly sophisticated models to evaluate peak broadening effects. This paper will provide a review of the state of art of local strain measurements by x-rays, discuss their limitations, provide an outlook of where the field may be going within the next years and address the most important issues to be solved. Examples will be given for the current limits in terms of resolution in time, space, strain and intensity.

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