scholarly journals Combing electron diffraction techniques for structure solution

2014 ◽  
Vol 70 (a1) ◽  
pp. C369-C369
Author(s):  
Andrew Stewart
Keyword(s):  
Electron Diffraction ◽  
Electron Diffraction Data ◽  
Data Sets ◽  
Data Set ◽  
Space Group ◽  
X Ray ◽  
Structure Solution ◽  
Convergent Beam ◽  
Beam Diffraction ◽  
Convergent Beam Diffraction

The last few years have seen a revolution in the field of 3D electron diffraction or diffraction tomography. We have moved from only acquiring a few low index zone axis patterns to full tomographic data sets recording all accessible areas of reciprocal space. These new larger data sets have made it easier for structure solution techniques such as direct methods from the x-ray world to be applied to the electron diffraction data for structure solution. While structure solution with tomographic electron diffraction is non trivial when compared to the x-ray case it is significantly easier than it was a few years ago. Mugnaioli et al. We are now in a situation where the most difficult and time consuming step can be the assignment of the space group to a data set. Electron diffraction has many advantages over the x-ray case in terms of the manner in which we can manipulate the electron beam. This allows the collection to convergent beam diffraction (CBD) or large angle convergent beam diffraction (LACBED) patterns, via the recently developed technique by Beanland et al. These techniques can make the assignment of space group significantly easier affair, and the path to structure solution a lot smoother. We will present the combination of data from tomographic, selected area (SA) and nano-beam (NBD) datasets, with diffraction from tomographic LACBED experiments where using the strengths of each technique can be leveraged for a much quicker route to structure solution.

Thickness dependence of the intensities of the 200 forbidden reflections in the TiBe2 diamond type structure

1988 ◽  
Vol 46 ◽  
pp. 826-827
Author(s):  
Dang-Rong Liu ◽  
D. B. Williams
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Convergent Beam Electron Diffraction ◽  
Type Structure ◽  
Beam Electron ◽  
Space Group ◽  
X Ray ◽  
Electron Diffraction Technique ◽  
Convergent Beam ◽  
Diamond Type

It is interesting to note that for the diamond type structure of Si, Ge and diamond, the forbidden {200} reflections in the exact <100> orientation diffraction pattern cannot be seen. In contrast, we also note a standing controversy over the structure of the MgAl2O4, spinel. Its structure was determined long ago by x-ray powder method as Fd3m (the diamond type). However, its electron diffraction pattern taken in the <100> orientation shows weak {200} reflections, which are taken as evidence that the spinel should have the space group F43m (the blende type), rather than Fd3m. Others speculate that these {200} reflections result from the high order Laue zone (HOLZ) reflections, and the spinel should be Fd3m. Nevertheless, still others think that these analyses are not conclusive. We have carefully studied the space group of TiBe2 using the convergent beam electron diffraction technique, and unambiguously demonstrated that its space group must be Fd3m.

Computer-aided orientation relationship determination in non-cubic systems

1986 ◽  
Vol 44 ◽  
pp. 692-693
Author(s):  
J. R. Porter
Keyword(s):  
Electron Diffraction ◽  
Orientation Relationship ◽  
Polycrystalline Material ◽  
Electron Diffraction Data ◽  
Classical Electron ◽  
Angle Pair ◽  
Convergent Beam ◽  
Cubic Systems ◽  
Alpha Alumina ◽  
Beam Diffraction

Classical electron diffraction techniques for determining the orientations of grains within a polycrystalline material are time consuming. However, many of the steps involved in the process of indexing a convergent beam diffraction (CBED) pattern, eliminating the 180° ambiguity and establishing an axis-angle pair orientation relationship are ideally suited to microcomputer assistance, especially when working with non-cubic systems. The procedure described is an off-line technique applied to a study of alpha alumina, for which extensive electron diffraction data has recently been compiled.

On the quality of the continuous rotation electron diffraction data for accurate atomic structure determination of inorganic compounds

2018 ◽  
Vol 51 (4) ◽  
pp. 1094-1101 ◽  
Author(s):  
Yunchen Wang ◽  
Taimin Yang ◽  
Hongyi Xu ◽  
Xiaodong Zou ◽  
Wei Wan
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Diffraction Data ◽  
Structural Models ◽  
Electron Diffraction Data ◽  
Data Sets ◽  
X Ray Diffraction ◽  
X Ray ◽  
Continuous Rotation

The continuous rotation electron diffraction (cRED) method has the capability of providing fast three-dimensional electron diffraction data collection on existing and future transmission electron microscopes; unknown structures could be potentially solved and refined using cRED data collected from nano- and submicrometre-sized crystals. However, structure refinements of cRED data using SHELXL often lead to relatively high R1 values when compared with those refined against single-crystal X-ray diffraction data. It is therefore necessary to analyse the quality of the structural models refined against cRED data. In this work, multiple cRED data sets collected from different crystals of an oxofluoride (FeSeO3F) and a zeolite (ZSM-5) with known structures are used to assess the data consistency and quality and, more importantly, the accuracy of the structural models refined against these data sets. An evaluation of the precision and consistency of the cRED data by examination of the statistics obtained from the data processing software DIALS is presented. It is shown that, despite the high R1 values caused by dynamical scattering and other factors, the refined atomic positions obtained from the cRED data collected for different crystals are consistent with those of the reference models refined against single-crystal X-ray diffraction data. The results serve as a reference for the quality of the cRED data and the achievable accuracy of the structural parameters.

scholarly journals UsingFOCUSto solve zeolite structures from three-dimensional electron diffraction data

2013 ◽  
Vol 46 (4) ◽  
pp. 1017-1023 ◽  
Author(s):  
Stef Smeets ◽  
Lynne B. McCusker ◽  
Christian Baerlocher ◽  
Enrico Mugnaioli ◽  
Ute Kolb
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Three Dimensional ◽  
Direct Methods ◽  
Electron Diffraction Data ◽  
Chemical Information ◽  
Data Sets ◽  
Dimensional Electron ◽  
Specific Chemical ◽  
Structure Solution

The programFOCUS[Grosse-Kunstleve, McCusker & Baerlocher (1997).J. Appl. Cryst.30, 985–995] was originally developed to solve zeolite structures from X-ray powder diffraction data. It uses zeolite-specific chemical information (three-dimensional 4-connected framework structure with known bond distances and angles) to supplement the diffraction data. In this way, it is possible to compensate, at least in part, for the ambiguity of the reflection intensities resulting from reflection overlap, and the program has proven to be quite successful. Recently, advances in electron microscopy have led to the development of automated diffraction tomography (ADT) and rotation electron diffraction (RED) techniques for collecting three-dimensional electron diffraction data on very small crystallites. Reasoning that such data are also less than ideal (dynamical scattering, low completeness, beam damage) and that this can lead to failure of structure solution by conventional direct methods for very complex zeolite frameworks,FOCUSwas modified to accommodate electron diffraction data. The modified program was applied successfully to five different data sets (four ADT and one RED) collected on zeolites of different complexities. One of these could not be solved completely by direct methods but emerged easily in theFOCUStrials.

The Suppression of Contamination in the Convergent-Beam Electron Diffraction Camera

1977 ◽  
Vol 32 (11) ◽  
pp. 1326-1327 ◽  
Author(s):  
W. C. T. Dowell ◽  
P. Goodman
Keyword(s):  
Electron Diffraction ◽  
Vapour Phase ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Specimen Temperature ◽  
Surface Migration ◽  
Before And After ◽  
Convergent Beam ◽  
Beam Diffraction ◽  
Convergent Beam Diffraction

Abstract It has been demonstrated that specimen contamination in convergent-beam diffraction operation can be prevented by maintaining the specimen temperature between -110 °C and -165 °C, without the use of especially high or clean vacuum conditions. At these temperatures, surface migration of molecules causing contamination is evidently inhibited. Precautions to prevent deposition from the vapour phase both before and after cooling are also required.

Supercell and subcell description of the crystal structure of triammonium bis(O-phospho-L-serinate) trihydrate

2006 ◽  
Vol 62 (5) ◽  
pp. 919-925 ◽  
Author(s):  
Małgorzata Hołyńska ◽  
Iwona Bryndal ◽  
Tadeusz Lis
Keyword(s):  
Crystal Structure ◽  
Diffraction Pattern ◽  
Water Molecules ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
Data Set ◽  
Space Group ◽  
X Ray ◽  
Average Structure ◽  
Structure Solution

The X-ray diffraction pattern obtained for a crystal of triammonium bis(O-phospho-L-serinate) trihydrate at 100 K displays the presence of weak superstructure reflections with odd l indices. Omission of the superstructure reflections leads to orthorhombic Laue symmetry. The structure may be solved and refined in the space group P212121 as an average structure omitting the weak reflections. The model reveals the presence of O-phospho-L-serinate monoanions, ammonium cations and partly disordered water molecules. The structure solution for the whole data set could be obtained only in the space group P21. There are two monoanions and two dianions of O-phospho-L-serinate per asymmetric unit, as well as six ordered ammonium cations and six water molecules.

Structure analysis of montmorillonite crystallites by convergent-beam electron diffraction

Clay Minerals ◽  
2005 ◽  
Vol 40 (1) ◽  
pp. 1-13 ◽  
Author(s):  
T. Beermann ◽  
O. Brockamp
Keyword(s):  
Electron Diffraction ◽  
Convergent Beam Electron Diffraction ◽  
Least Square ◽  
Data Set ◽  
Beam Electron ◽  
X Ray ◽  
Kinematic Theory ◽  
Vacancy Distribution ◽  
Diffraction Patterns ◽  
Convergent Beam

AbstractThe small particle size and the random stacking of layers has previously hindered systematic structure investigations of montmorillonite. By applying the convergent-beam electron diffraction mode (CBED) of a transmission electron microscope (TEM) with a beam spot of ~800 Å we were able to examine undisturbed areas of montmorillonite crystallites.Because montmorillonite crystallites are mostly thin particles, kinematic theory can be applied and the CBED patterns can be interpreted directly, provided that the particle thickness remains below the critical value of 350 Å. An average thickness of ~90 Å was calculated here for montmorillonite of bulk samples from X-ray diffraction analysis and lattice-fringe images. However, satisfactory diffraction intensity patterns for quantitative evaluation were obtained only from crystallites with a thickness above the average, which yielded a sufficient scattering volume. These patterns could be described in terms of the kinematic theory and therefore these crystallites were <350 Å thick. Yet, crystallites of adequate thickness were extremely rare in the three samples investigated (Clay Spur, Rock River and Upton, all in Wyoming, USA).The diffraction intensities from the ab plane of single montmorillonite crystallites of the various origins fit the three structural models for a trans-vacancy distribution, a cis-vacancy distribution or a random-cation distribution within the octahedral sheets. The configuration of the diffraction patterns also shows a 1M symmetry of the layer. Due to the limited data set of CBED patterns, a refinement of the structure could not be achieved. However, energy dispersive X-ray spectroscopy data and computation of the cation–anion distances and valences using the ‘distance valence least square’ program permitted a refinement of the models.

The structure of nano-twinned rhombohedral YCuO2.66 solved by electron crystallography

2019 ◽  
Vol 75 (1) ◽  
pp. 107-112 ◽  
Author(s):  
Holger Klein ◽  
V. Ovidiu Garlea ◽  
Céline Darie ◽  
Pierre Bordet
Keyword(s):  
Electron Diffraction ◽  
Two Dimensions ◽  
Electron Diffraction Data ◽  
Electron Crystallography ◽  
One Dimensional ◽  
X Ray ◽  
Spin Interactions ◽  
Structure Solution ◽  
Precession Electron Diffraction ◽  
Frustrated Spin

In the search for frustrated spin interactions, a YCuO2.66 phase has been synthesized by a treatment under oxygen pressure of YCuO2.5. X-ray powder diffraction and electron diffraction studies have been conducted. Electron diffraction shows that the sample is twinned on a 10 nm scale. Precession electron diffraction data obtained from a twinned crystal was treated in order to obtain intensities corresponding to only one of the orientations of the twins. From this data a structure solution was obtained where, as in YCuO2.5, the Cu atoms form triangular planes. The Cu atoms are linked in two dimensions by oxygen atoms in the present structure whereas in YCuO2.5 they are only linked in one-dimensional chains.

scholarly journals Quasicrystal approximants solved by Rotation Electron Diffraction (RED)

2014 ◽  
Vol 70 (a1) ◽  
pp. C1195-C1195 ◽  
Author(s):  
Sven Hovmöller ◽  
Devinder SINGH ◽  
Wei Wan ◽  
Yifeng Yun ◽  
Benjamin Grushko ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Data Processing ◽  
Single Crystal ◽  
Crystal Structures ◽  
Reciprocal Lattice ◽  
Electron Diffraction Data ◽  
Data Set ◽  
X Ray ◽  
X Ray Crystallography ◽  
3D Electron

We have developed single crystal electron diffraction for powder-sized samples, i.e. < 0.1μm in all dimensions. Complete 3D electron diffraction is collected by Rotation Electron Diffraction (RED) in about one hour. Data processing takes another hour. The crystal structures are solved by standard crystallographic techniques. X-ray crystallography requires crystals several micrometers big. For nanometer sized crystals, electron diffraction and electron microscopy (EM) are the only possibilities. Modern transmission EMs are equipped with the two things that are necessary for turning them into automatic single crystal diffractometers; they have CCD cameras and all lenses and the sample stage are computer-controlled. Two methods have been developed for collecting complete (except for a missing cone) 3D electron diffraction data; the Rotation Electron Diffraction (RED) [1] and Automated Electron Diffraction Tomography (ADT) by Kolb et al. [2]. Because of the very strong interaction between electrons and matter, an electron diffraction pattern with visible spots is obtained in one second from a submicron sized crystal in the EM. By collecting 1000-2000 electron diffraction patterns, a complete 3D data set is obtained. The geometry in RED is analogous to the rotation method in X-ray crystallography; the sample is rotated continuously along one rotation axis. The data processing results in a list of typically over 1000 reflections with h,k,l and Intensity. The unit cell is typically obtained correctly to within 1%. Space group determination is done as in X-ray crystallography from systematically absent reflections, but special care must be taken because occasionally multiple electron diffraction can give rise to very strong forbidden reflections. At +/-60° tilt with 0.1° steps, a complete data collection will be some 1200 frames. With one second exposures this takes about one hour. There is no need to align the crystal orientation. The reciprocal lattice can be rotated and displayed at any direction of view. Sections such as hk0, hk1, hk2, h0l and so on can easily be cut out and displayed. We have solved over 50 crystal structures by RED in one year. These include the most complex zeolites ever solved and quasicrystal approximants, such as the pseudo-decagonal approximants PD2 [3] and PD1 in AlCoNi. Observed and calculated sections of reciprocal space (cut at 1.0Å) are shown in Fig. 1. Notice the 10-fold symmetry of strong reflections.

Sign in / Sign up

Export Citation Format

Share Document