Search results for " diffraction"
showing 10 items of 896 documents
Towards automated diffraction tomography: Part I—Data acquisition
2007
Abstract The ultimate aim of electron diffraction data collection for structure analysis is to sample the reciprocal space as accurately as possible to obtain a high-quality data set for crystal structure determination. Besides a more precise lattice parameter determination, fine sampling is expected to deliver superior data on reflection intensities, which is crucial for subsequent structure analysis. Traditionally, three-dimensional (3D) diffraction data are collected by manually tilting a crystal around a selected crystallographic axis and recording a set of diffraction patterns (a tilt series) at various crystallographic zones. In a second step, diffraction data from these zones are com…
Ab Initio Structure Determination of Vaterite by Automated Electron Diffraction
2012
tion that is fundamental for understanding material properties. Still, a number of compounds have eluded such kinds of analysis because they are nanocrystalline, highly disordered, with strong pseudosymmetries or available only in small amounts in polyphasic or polymorphic systems. These materials are crystallographically intractable with conventional Xray or synchrotron radiation diffraction techniques. Single nanoparticles can be visualized by high-resolution transmission electron microscopy (HR-TEM) up to sub�ngstrom resolution, [2] but obtaining 3D information is still a difficult task, especially for highly beam-sensitive materials and crystal structures with long cell parameters. Elec…
On the existence of a pyrochlore-type phase in the system Bi2O3–TiO2
1995
The existence of a bismuth titanate in the range between Bi 2 Ti 4 O 11 (Bi 2 O 3 . 4 TiO 2 ) and Bi 4 Ti 3 O 12 (2 Bi 2 O 3 . 3 TiO 2 ) has been investigated by X-ray diffraction of samples prepared by solid state reactions. For reaction temperatures above 1100 °C and a starting composition Bi 2 O 3 . 2 TiO 2 there appeared additional lines which could be attributed to a cubic face-centred cell with a = 10.354 A. A multiphase Rietveld analysis based on X-ray powder diffraction data confirmed the structural model of a pyrochlore for this compound. There is evidence that this phase belongs to the group of defect pyrochlores with a Bi 3+ -deficiency resulting in a composition of Bi 1.833 Ti 2…
Isomerism in [MCl2(ERR‘)2] (M = Pd, Pt; E = S, Se; R, R‘ = Me, Ph)
2006
A series of thioether and selenoether complexes [MCl2(EPh2)2] and [MCl2(SMePh)2] (M = Pt, Pd; E = S, Se) have been prepared and characterized to explore the isomerism of the complexes in solution and in the solid state. The NMR spectroscopic information indicates that only one isomer is present in solution in case of the palladium complexes, while two isomers are formed in the case of most platinum complexes. Single-crystal X-ray structures of trans-[PdCl2(SPh2)2] (1t), trans-[PdCl2(SePh2)2] (2t), cis-[PtCl2(SePh2)2] (4c), trans-[PdCl2(SMePh)2] (5t), and trans-[PtCl2(SMePh)2] (7t) are reported and have been used as starting points for the X-ray powder diffraction structure determinations us…
Liquid Structure of Trihexyltetradecylphosphonium Chloride at Ambient Temperature: An X-ray Scattering and Simulation Study
2009
We report on an experimental and simulation study done on a representative room temperature ionic liquid, namely tetradecyltrihexylphosphonium chloride, at ambient conditions. The study was conducted using small and wide angle X-ray scattering and molecular dynamics simulations. Both approaches converge in indicating that this material is characterized by the existence of strong P-Cl interactions (with characteristic distances between 3.5 and 5.0 Å) and by the occurrence of nanoscale segregation, despite the symmetric nature of the cation and similarly to other room temperature ionic liquids. A good agreement is found between the structure factor and pair correlation functions obtained from…
X-ray diffraction line broadening on vibrating dry-milled Two Crows sepiolite
2006
A reference sample of sepiolite and products of its comminution by vibrating dry-milling have been studied using X-ray diffraction (XRD) line-broadening analysis, complementary field emission scanning electron microscopy (FESEM) images and surface area measurements. The apparent crystallite sizes determined via XRD are in agreement with observations on FESEM images. The sepiolite aggregates consist of lath-shaped agglutinations of prisms and pinacoids elongated along [001], each lath including several crystallites in that direction. The surface area magnitudes are in the range of previous experimental measurements of other sepiolites. The results obtained show the effectiveness of vibro-mil…
Investigation of Silicon Carbide Polytypes by Raman Spectroscopy
2014
Abstract Polytypes of colourless and coloured single crystals of silicon carbide (SiC) grown on SiC substrates by chemical vapour deposition are studied using Raman spectroscopy supplemented by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The SEM analysis of the defect stacking faults, inclusions of defects and their distribution has shown that they correlate with the peak positions of the obtained Raman spectra and with the XRD data on the crystal structure
Non-Conventional Tunable Spatial Filtering
1987
A virtual display of the Fraunhofer diffraction pattern of any object is formed in the transverse source plane by theyirtual diffracted rays extqn0ing in the region to the left of the screen containing the transparencyl),2). Except for a few cases '')"°), the concept of virtual Fourier transform appears not to have been made use of. The main idea of this paper is, bearing in mind the property referred to in the above paragraph, to describe a novel spatial filtering technique. In this way, one can obtain different filtered images, by simply moving the point source along the optical axis. The basic theory is described below.
Structural and elastic properties of defect chalcopyrite HgGa2S4 under high pressure
2014
In this work, we focus on the study of the structural and elastic properties of mercury digallium sulfide (HgGa2S4) at high pressures. This compound belongs to the family of AB(2)X(4) ordered-vacancy compounds and exhibits a tetragonal defect chalcopyrite structure. X-ray diffraction measurements at room temperature have been performed under compression up to 15.1 GPa in a diamond anvil cell. Our measurements have been complemented and compared with ab initio total energy calculations. The axial compressibility and the equation of state of the low-pressure phase of HgGa2S4 have been experimentally and theoretically determined and compared to other related ordered-vacancy compounds. The pres…
The Significance of Ionic Bonding in Sulfur Dioxide: Bond Orders from X-ray Diffraction Data
2012
A novel refinement technique for X‐ray diffraction data has been employed to derive S-O bond orders in sulfur dioxide experimentally. The results show that ionic S-O bonding dominates over hypervalency.