Anisotropic diffraction peak broadening and dislocation substructure in hydrogen-cycled LaNi₅ and substitutional derivatives

Hydrogen absorption–desorption cycling in LaNi₅ and substitutional derivatives induces anisotropic diffraction peak broadening. The change of the anisotropy as a function of substitution (by Co, Mn, Al, Fe, Cu, Sn and Ce) is discussed in terms of various dislocation substructures.

Corrections for surface X-ray diffraction measurements using the Z-axis geometry: finite size effects in direct and reciprocal space

Two approaches to the correction of grazing-incidence X-ray diffraction data are described: one taking into account the evolution of the diffracting area during an ω scan; the other considering the case of finite-width rods, under the point-like sample approximation. A full numerical simulation is also presented.

X-ray diffraction from perfect silicon crystals distorted by surface acoustic waves

High-resolution X-ray diffraction measurements were carried out on ZnO/Si devices under surface acoustic wave excitation and revealed some very clear satellite diffraction peaks that are obtained from the sinusoidal modulation of the near-surface region. This experiment shows that the propagation of a Rayleigh surface acoustic wave in a perfect crystal acts as a dynamical diffraction grating.

X-ray topographic determination of the granular structure in a graphite mosaic crystal: a three-dimensional reconstruction

Section topographs recorded at different spatial locations and at different rocking angles of a highly oriented pyrolytic graphite crystal allow three-dimensional maps of the local angular-dependent scattering power to be obtained. The maps allow the extraction of information on local structural parameters such as size, form and internal mosaic spread of crystalline domains, and represent a new approach to the characterization of mosaic crystals.

Novel image analysis of two-dimensional X-ray fiber diffraction patterns: example of a polypropylene fiber drawing study

On-line X-ray studies of structural development during continuous polypropylene fiber drawing were carried out using synchrotron radiation. A unique image analysis method was introduced to extract quantitative information on the crystal, amorphous and mesomorphic fractions.

Study of disorder in a tetragonal tungsten bronze ferroelectric relaxor: a structural approach

Electron diffraction analysis, nuclear magnetic resonance measurements, structural determination and refinements were performed on two ferroelectric lead-containing ceramics (classical and relaxor), with tetragonal tungsten bronze structure, in order to investigate the origin of the relaxor behaviour in such compounds.

High-energy X-ray diffuse scattering using Weissenberg flat-cone geometry

A description of a diffuse X-ray scattering measurement technique using high-energy X-rays in Weissenberg flat-cone geometry is presented.

Double-crystal diffraction imaging with a small effective divergence source: application to the magneto-acoustic vibrations in FeBO₃

Ultrasonic standing waves, excited in FeBO₃ (111) crystal plates through magneto-elastic coupling, have been visualized using monochromatic Bragg diffraction imaging (topography) employing synchrotron radiation. The images depend strongly on whether diffraction by the sample occurs in the same plane as in the double-crystal monochromator, or in the perpendicular plane.

New methods for diffraction stress measurement: a critical evaluation of new and existing methods

New methods of diffraction stress analysis of polycrystalline materials, consisting of cubic elastically anisotropic crystallites, are proposed and compared with existing methods. The new methods do not require diffraction elastic constants.

The crystal neutron diffractometer resolution function, spatial effects included

A procedure for computing the resolution function for a crystal neutron diffractometer, taking into account the spatial configuration of the experimental setup and the monochromator curvature, is presented.

Etude structurale d'un hydrate 10 Å instable de kaolinite

The treatment of KGa-1 kaolinite with dimethyl sulfoxide and ammonium fluoride heated at 383 K provides an unstable hydrated phase characterized by a 10 Å basal distance; when air-dried, this hydrate gives a dehydrated phase at 7.15 Å. This hydrate has been structurally characterized via a comparison between experimental and calculated X-ray diffraction profiles.

Using a prism to reject or select harmonic reflections in an X-ray monochromator

X-ray refraction by a prism has been used to discriminate between different harmonic orders of a two-crystal monochromator. Rejection of higher-order harmonics and selection of specific harmonic order is demonstrated.

Global least-squares determination of Eulerian angles from single electron diffraction patterns of tilted crystals

A least-squares procedure is used to determine the orientation of a crystal in a tilted diffraction geometry from a single electron diffraction pattern. The scheme can be universally applied to crystals with one, only a few, or many crystallographic layers and yields highly accurate Eulerian angles of the diffraction geometry.

Determination of lattice-transform density profiles for multilayered three-dimensional microcrystals in electron crystallography

Applying least-squares and correlation methods it is possible to separate the shape of the reciprocal lattice from the molecular transform using a single electron diffraction pattern. This separation is one crucial step in the structure determination of beam-sensitive multilayered three-dimensional microcrystals.

Contrast analysis of the composition of ribosomes extracted with different purification procedures

The composition and hydration of E. coli ribosomes isolated with different purification protocols has been analysed by combining two experimental techniques: measurements of small-angle neutron scattering, for two different isotopic solvent compositions, and refractive index increments.

Measurement of the fine structure factors and extinction distance by convergent-beam electron diffraction in Co₃Ti with and without B doping

Using convergent-beam electron diffraction (CBED), the fine structure factors of Co₃Ti alloys have been measured and the effects of boron microalloying on the fine structure factors have been studied. The extinction distances of Co₃Ti have been obtained by both Kelly's method and the CBED simulation method.

Calculation of diffraction line profiles from specimens with dislocations. A comparison of analytical models with computer simulations

A method is proposed to calculate diffraction line profiles from specimens with dislocations. Calculated results are compared to results obtained from analytical models.

Data smoothing and distortion of X-ray diffraction peaks. I. Theory

Smoothing distortions of an X-ray diffraction peak are theoretically analysed and formulae to calculate the smoothing-induced changes of all parameters of a peak are derived.

Data smoothing and distortion of X-ray diffraction peaks. II. Application

Based on the analysis of geometric relations, it is found that the amplitude of the distortion of the full width at half-maximum (FWHM) of a peak after smoothing is the largest among the distortions of the seven parameters of a peak: maximum intensity, FWHM, shape, asymmetry, integral intensity, peak position and integral width. It is found that the smoothing-induced distortions of an actual X-ray diffraction peak trend towards those of ideal curves.

Reporting and evaluating absolute-structure and absolute-configuration determinations

Detailed practical and numerical information is provided for undertaking and evaluating absolute-structure and absolute-configuration determinations.

Periodically poled KTA crystal investigated using coherent X-ray beams

The distribution of inverted ferroelectric domains on the surface and within the bulk of a periodically poled KTA single crystal has been observed using a simple synchrotron X-ray diffraction imaging setup. This technique allows one to reveal the phase difference between the waves that are Bragg diffracted from adjacent domains via free-space propagation (Fresnel diffraction).

Computing in macromolecular crystallography using a parallel architecture

Calculations in macromolecular crystallography inherently have a high degree of parallelism. The OpenMP programming interface can be used in crystallographic programs to reduce computation times on multiprocessor computers.

Experimental determination of the instrumental transparency function of texture goniometers

The instrumental transparency functions of five commercially available texture goniometers were measured with highly perfect, monocrystalline silicon samples. The transparency function is the fundamental characteristic of a texture goniometer, defining its angular resolving power.

High-pressure studies of the cubic to rhombohedral transformation in NbO₂F

A detailed study of the cubic to rhombohedral high-pressure transition of NbO₂F has been performed by powder diffraction using synchrotron X-ray radiation and diamond anvil cells, showing that the transition starts at 0.28 and is complete at 0.65 GPa.

LAPODS: a computer program for refinement of lattice parameters using optimal regression

LAPODS is an upgraded version of the program LAPOD for the refinement of lattice parameters. It has several new features, including automatic determination of significant systematic errors, based on statistical considerations.

New techniques for indexing: N-TREOR in EXPO

New techniques are described for indexing a powder pattern. The program, an evolution of TREOR90, has been integrated into the package EXPO.

BEAM-ish: a graphical user interface for the physical characterization of macromolecular crystals

BEAM-ish is a graphical user interface that manages the processing of multiple super-fine φ-sliced diffraction images and seamlessly integrates several programs for mosaicity calculations.

Development of a graphical interface for the Rietveld refinement program DBWS

The program DBWS Tools is an application for DBWS users that compiles input control files for versions 9411 and 9807 and manages program execution using a Windows 95/98/NT interface.

SUBGROUPGRAPH: a computer program for analysis of group–subgroup relations between space groups

The main aim of SUBGROUPGRAPH is a detailed study of a group–subgroup relation between two space groups, G > H, including the construction of chains of maximal subgroups for G > H for a specified/non-specified index i = |G:H| (the so-called G–H graph), the determination of the number of the different H_k < G, H_k ≅ H, and their distribution into classes of conjugate subgroups relative to G, etc.

PDFgetN: a user-friendly program to extract the total scattering structure factor and the pair distribution function from neutron powder diffraction data

This program allows S(Q) and the pair-distribution function to be determined from a variety of time-of-flight neutron powder diffractometers. Features are a graphical user interface and permanent storage of processing parameters.

TOPOS3.2: a new version of the program package for multipurpose crystal-chemical analysis

The program package TOPOS is intended for the automation of all stages of crystal-chemical analysis.

Comment on CRUNCH: a phase refinement program for high-resolution macromolecular structures by Langs, Blessing & Smith (2000)

Comment on Langs, Blessing & Smith [J. Appl. Cryst. (2000), 33, 174–175].

Response to de Graaff & de Gelder's comment on CRUNCH: a phase refinement program for high-resolution macromolecular structures

Response to comment on Langs, Blessing & Smith [J. Appl. Cryst. (2000), 33, 174–175].

Jerry B. Cohen

European Crystallography Prize

Forthcoming meetings and short courses