A new format and overall appearance for Journal of Applied Crystallography

Editorial.

Study of the influence of oxygen on structural perfection of silicon single crystals by high-resolution X-ray diffraction and infrared absorption measurements

The crystalline perfection of silicon crystals grown by the float zone (FZ) method is generally slightly lower than that of crystals grown by the Czochralski (Cz) technique, which have higher oxygen content. High-resolution X-ray diffraction studies and infrared-absorption measurements have shown that, if the level of oxygen in FZ silicon crystals is increased by annealing, from 1.3 × 10¹⁷ to 13 × 10¹⁷ atoms cm (typical values for Cz crystals), the degree of perfection of FZ crystals increases remarkably, approaching that of the Cz crystals.

New developments of computer-aided crystallographic analysis in transmission electron microscopy

A computer program for on-line crystal orientation measurements based on spot and Kikuchi electron diffraction patterns in TEM is presented. The program facilitates the complete characterization of lattice defects, such as dislocations and grain boundaries.

Contribution to residual-stress evaluation in high-stress-gradient zones by X-ray diffraction

A new strategy to analyse both the mechanical and the metallurgical state in high-stress gradient zones is proposed. The measurement and treatment methods have been adapted and a complete modelling of the X-ray source has been developed to account for the local intensity distribution.

Correction of specimen absorption in X-ray diffuse scattering experiments with area-detector systems

Methods for the correction of specimen absorption, dedicated to two-dimensional area-detector systems and broad diffuse scattering phenomena, are implemented and tested. Synchrotron radiation diffraction experiments and numerical calculations are used to study the influence of experimental parameters on the accuracy of the absorption correction which is applied pixel-wise.

Three-beam interference measurements with a six-circle κ diffractometer

The feasibility of a specific six-circle κ diffractometer for measuring three-beam interference profiles is outlined.

Integration procedure for the qu­antitative analysis of dispersive anomalous diffraction

Dispersive diffraction allows the simultaneous measurement of diffracted intensities over an energy range. This method has been developed and a procedure for the quantitative integration of dispersive diffraction images for continuous (DAFS-like) and discrete (MAD-like) experiments is described.

Study of thermal behaviour of 30Li₂O·70TeO₂ glass by X-ray dynamic observation

The dynamical structural changes of 30Li₂O·70TeO₂ glass were mainly studied by in situ high-temperature X-ray diffraction. The phase transitions of lithium tellurite at high temperature were clarified, including reversible changes between α-Li₂Te₂O₅ and β-Li₂Te₂O₅.

X-ray diffraction study of polycrystalline p-chloro­nitro­benzene

The X-ray diffraction pattern of powdered 1-Cl-4-NO₂-benzene was measured at several temperatures in order to characterize the structure of two different phases.

Accuracy of molecular structures determined from high-resolution powder diffraction. The example of m-fluoro­benzoic acid

The accuracy with which it is possible to determine atomic coordinates of light atoms at arbitrary positions using X-ray powder data alone is demonstrated. The results are compared with those of a single-crystal study on the same compound.

Nanopowder diffraction analysis beyond the Bragg law applied to palladium

Tools for nanopowder diffraction analysis, based on simulation, are proposed.

Crystal structure refinement of α-Si₃N₄ using synchrotron radiation powder diffraction data: unbiased refinement strategy

The crystal structure of α-silicon nitride (Si₃N₄) was refined by the Rietveld method using synchrotron radiation powder diffraction data. A refinement procedure using a new weight function for least-squares fitting was studied, and guidelines for an unbiased refinement procedure were derived.

Diffraction-line shift caused by residual stress in polycrystal for all Laue groups in classical approximations

Expressions are derived within the Voigt and Reuss approximations, describing the anisotropic diffraction-line shift caused by the elastic strain in isotropic polycrystals. These expressions, appropriate for the Rietveld programs, are different for different Laue groups.

A tool for X-ray diffraction analysis of thin layers on substrates: substrate peak removal method

A method is proposed that removes from a diffraction pattern, in which overlapping peaks of a thin layer and a substrate are present, the substrate peaks, using a separate measurement of an uncovered substrate. The method is shown to yield good results for a TiN layer deposited on a tool-steel substrate.

Sample geometry effects on incoherent small-angle scattering of light water

It is shown that the scattering intensities of light water collected with different ratios of sample-to-beam dimension present large differences as a function of sample thickness. In particular, ratios smaller and larger than unity are considered and the results are discussed and compared with Monte Carlo simulations.

Double monochromator with three pairs of crystals for a SANS machine: Monte Carlo simulation studies

Monte Carlo calculations for the resolution and intensity of a double-crystal monochromator system for a small-angle neutron scattering machine are presented. The relative merits of this monochromator as compared to our available monochromators are discussed.

Origin of the optical activity of silver thiogallate

The birefringence and optical activity of AgGaS₂ have been determined using a high-accuracy universal polarimeter. The data are compared with those of previous works and the connection between the optical properties and crystal structure is discussed.

On the instrumental resolution in X-ray reflectivity experiments

A general form of the instrumental resolution function is given for X-ray reflectivity experiments.

Instrumental line shapes in neutron powder diffraction with focusing monochromators

The assumption of Gaussian line shapes and Caglioti profile functions leads to a good quality of fit in whole-pattern refinements, not only with conventional instruments, but also with focusing instruments. The quality of the fit improved on approximating instrumental line shapes with double cumulative functions.

Position-sensitive analysis in curved-crystal three-axis neutron spectrometry (quasielastic scattering case)

The use of bent perfect crystals in three-axis neutron spectroscopy with position-sensitive detection is analysed. High intensities at high resolutions are achievable through focusing in scattering combined with `thickness focusing' from multilamella analysers.

Accurate structure-factor measurements using high-energy synchrotron radiation: a test on cuprite, Cu₂O

Structure factors were measured for cuprite, Cu₂O, using 100 keV synchrotron radiation, with an accuracy that allowed full multipole refinements.

A cryocooling technique for protein crystals grown by dialysis from volatile solvents

This paper describes a cryocooling method, based on the use of dialysis adaptors for 24-well crystallization plates, that permits the transfer of crystals with greater ease and lower risk of mechanical damage.

Preparation of silver behenate coatings to provide low- to mid-angle diffraction calibration

Specimens of silver behenate that exhibit a high degree of preferred orientation have been prepared. Multiple (0 0 l) diffraction peaks, (0 0 1) to (0 0 48), are easily observed using a conventional laboratory X-ray diffraction instrument.

CRUNCH: a phase refinement program for high-resolution macromolecular structures

A phase refinement program for high-resolution macromolecular structures is described that may allow the mean phase error of an initial structure solution to be reduced before inspecting a map to see how well it may fit a structural model.

TOP: a new method for protein structure comparisons and similarity searches

In order to facilitate the three-dimensional structure comparison of proteins, software for making comparisons and searching for similarities to protein structures in databases has been developed.

MarqX: a new program for whole-powder-pattern fitting

MarqX can be used for an unconstrained profile fitting (pattern decomposition) or constrained modelling of the whole powder pattern (Pawley method), for single- as well as multiple-phase samples.

Crystallographic Instrumentation

New Cryostream Cooler

Notes for Authors

Forthcoming meetings and short courses