Analysis of Diffuse Scattering from Single Crystals via the Reverse Monte Carlo Technique. I. Comparison with Direct Monte Carlo

We compare the use of the reverse Monte Carlo (RMC) technique for analysing diffuse scattering data from single crystals with the well established direct Monte Carlo (MC) method. We further describe attempts to use RMC to obtain short-range correlation information for a relatively simple real physical system, the Tl cation distribution in TlSbOGeO₄.

Analysis of Diffuse Scattering from Single Crystals via the Reverse Monte Carlo Technique. II. The Defect Structure of Calcium-Stabilized Zirconia

We report the results of an attempt to use reverse Monte Carlo (RMC) refinement to fit a model structure to the diffuse X-ray and neutron scattering of the complex defect structure of calcium-stabilized zirconia (Ca-CSZ), composition Zr_0.85- Ca_0.15O_1.85.

Site Occupancies in the Battery Electrode Material LaNi_3.55Mn_0.4Al_0.3Co_0.75 as Determined by Multiwavelength Synchrotron Powder Diffraction

The problem of determining the mixed occupancies of two crystallographic sites by four types of atom was solved by using the powder diffraction contrast produced by anomalous dispersion effects.

Weighting Scheme for the Minimization Function in Rietveld Refinement

A new weighting scheme for the minimization function used in the Rietveld method for structure refinement using powder diffraction data is proposed. It significantly improved the accuracy of positional parameters of test samples.

A Simple and Sensitive Method for Simultaneous High-Temperature X-ray Powder Diffraction and Thermogravimetric Analysis

An apparatus is described for simultaneous high-temperature X-ray powder diffraction and thermogravimetric studies, based on a Guinier–Lenné focusing powder camera and an analytical chemical balance. The technique is illustrated by a study of the dehydration reactions in an artists' plaster containing gypsum.

Observation of Phase change of X-ray Polarizability by Rocking Curves in the Bragg Case

Asymmetry and its reversal of the transmitted rocking curves in the Bragg case were measured for GaAs 600 below the Ga K absorption edge. The reversal was caused by the phase change of X-ray polarizability.

Modelling Dislocation-Induced Anisotropic Line Broadening in Rietveld Refinements Using a Voigt Function. I. General Principles

The theory of dislocation-induced X-ray or neutron diffraction line broadening developed by Krivoglaz et al. and Wilkens has been adapted for Rietveld refinement of the powder diffraction profile by fitting a Voigt function to each peak.

Modelling Dislocation-Induced Anisotropic Line Broadening in Rietveld Refinements Using a Voigt Function. II. Application to Neutron Powder Diffraction Data

The approach to the problem of modelling dislocation-induced X-ray or neutron-diffraction-line broadening developed in the previous paper is applied to the Rietveld refinement of the neutron powder diffraction profiles of deuterium-cycled LaNi₅ and β-PdD_0.66.

Small-Angle Scattering from Particles Having an Irregular Inner Structure

The small-angle scattering pattern of spherical particles having an inner structure composed of two randomly dispersed phases is derived. It is given as a sum of two functions: the scattering from isotropic particles of average density and a contribution of the inner inhomogeneities described by a single characteristic length.

Discovery of a New Boron-Rich Phase by Electron Crystallography

Boron powder, supplied as amorphous, was found to have a significant proportion of well crystallized particles. Examination of the crystalline particles by convergent-beam electron diffraction revealed that they had a previously unreported orthorhombic crystal structure that was determined as Pnma (a = 16.7, b = 17.7 and c = 10.3 Å).

Computer Simulation Approach to Reliability and Accuracy in Powder Diffraction Structure Refinement

The powder refinement of a population of simulated noisy patterns samples the frequency distribution of structural parameters and gives their statistical estimators (mean, dispersion, correlations).

Resonance time Modulation of X-ray Diffraction in Crystals Deformed by Ultrasound

A theory of frequency modulation of X-rays by ultrasound during dynamical diffraction in crystals is presented.

A Note on Elastic Scattering from Assemblies of Particles

The scattered intensity distribution from particle assemblies is related to the Fourier transform of the area fraction; by modifying the scattering density distribution in the particles, the deconvolution procedure used for obtaining the structure factor can be simplified.

Fits of the γ-MnO₂ Structure Model to Disordered Manganese Dioxides

A pyrolusite/ramsdellite intergrowth model is tested by fitting it to measured powder X-ray diffraction patterns of manganese dioxide. The model describes the structure of the investigated chemically prepared manganese dioxide well, but not the structure of the electrolytically prepared one.

The Practicality of Using a Three-Dimensional Fast Fourier Transform in Auto-Indexing Protein Single-Crystal Oscillation Images

Tests have demonstrated the practicality of using a three- dimensional fast Fourier transform calculation as the basis of an auto-indexing method for single protein crystal oscillation images.

A New Synchrotron-Based Diffraction Technique for Perturbation Crystallography

The speed and accuracy of measuring electric-field-induced changes in diffracted intensities has been improved by two orders of magnitude. This is done by combining broad-energy-band optics with lock-on detection techniques.

Diffraction Anomalous Fine Structure on Forbidden and Superlattice Reflections

The phenomenon of diffraction anomalous fine structure (DAFS) has been examined in relation to structural symmetry, and the role of DAFS signals is discussed with respect to highly absorbing crystals of finite size.

The 30 m Small-Angle Neutron Scattering Instruments at the National Institute of Standards and Technology

The design, performance and modes of operation of two 30 m small-angle neutron scattering instruments at the NIST Center for Neutron Research are described.

Image Plates as One-Dimensional Detectors in High-Resolution X-ray Diffraction

An image plate has been used as a detector for high-resolution X-ray diffraction of semiconductor heterostructures.

Eigen-System Analysis of X-ray Diffraction Profile Deconvolution Methods Explains Ill-Conditioning

An eigen-system analysis has been used to investigate ill- conditioning in various deconvolution methods applied to X-ray profiles. Terms that contribtue to the ill-conditioning of the solution profile are quantifed.

Bicrystallography of the Epitaxic Systems `III–V Nitrides on Sapphire': Theory and Experiment

By comparison of experimental data with theoretical considerations, it has been shown that most of the epitaxic orientation relationships for the `III–V nitrides on sapphire' system can be explained in terms of symmetrical analysis and Monte Carlo simulation of orientation distributions of primary nuclei.

Peak Decomposition using Pearson Type VII Function

An X-ray diffraction peak-decomposition procedure using a Pearson type VII function is described and implemented in a Microsoft Excel spreadsheet to aid a beginning student of X-ray diffraction.

Introduction to crystallography: two-dimensional computer simulations

An interactive tool for investigation of the real-space/reciprocal-space relationship in arbitrary two-dimensional crystal structures has been developed for teaching.

A reaction cell for in situ studies of hydrothermal titration

The design of a reaction cell for in situ studies of hydrothermal titration and ion-exchange reactions is presented.

Comment on Determination of a mean orientation from a cloud of orientations. Application to electron back-scattering pattern measurements by Humbert et al. (1996)

Comments are made on a paper by Humbert, Gey, Muller & Esling [J. Appl. Cryst. (1996), 29, 662-666]. Some inaccuracies in the formal approach to the calculation of the mean orientation are indicated.

See also Response to this Comment [J. Appl. Cryst. (1998). 31, 485].

Response to Morawiec's (1998) comment on Determination of a mean orientation from a cloud of orientations. Application to electron back-scattering pattern measurements

The authors had published two methods to compute the mean orientation from a cloud of orientations, as the problem practically arises when measuring individual orientations [Humbert, Gey, Muller & Esling (1996). J. Appl. Cryst. 29, 662-666]. This response recalls and outlines the main differences between their practical appproach and the more general mathematical problem exposed by Morawiec in his comments [Morawiec (1998). J. Appl. Cryst. 31, 484].

Comment on Probabilities of random disorientation axes in cubic polycrystals by Basson (1997)

Comments are made on a paper by Basson [J. Appl. Cryst. (1997), 30, 102-106]. Some misleading conclusions concerning the distribution of disorientation axes are clarified.

See also Response to this Comment [J. Appl. Cryst. (1998).

Response to Morawiec's (1998) comment on Probabilities of random disorientation axes in cubic polycrystals

Comments are given about a previous paper [Basson (1997). J. Appl. Cryst. 30, 102-106]. In particular, some details concerning the construction of the global distribution of disorientation axes in stereographic projection coordinates are discussed.

See also Comment to which this is a Response [J. Appl. Cryst. (1998). 31, 486].

Comment on Correlation effects in small-angle neutron scattering from closely packed spheres by Bertram (1996)

Comments are made on a paper by Bertram [J. Appl. Cryst. (1996), 29, 682-685].

See also Response [J. Appl. Cryst. (1998), 31, 489]

Response to Pedersen's (1998) comment on Correlation effects in small-angle neutron scattering from closely packed spheres

This note is a response to the comments made by Pedersen [J. Appl. Cryst. (1998), 31, 488-489] on the paper Correlation effects in small-angle neutron scattering from closely packed spheres by Bertram [J. Appl. Cryst. (1996), 29, 682-685].

Comment on Misorientation-angle distribution of randomly oriented symmetric objects by Morawiec (1995)

For crystallographic groups of rotations, the misorientation- angle distributions p(omega) given by Morawiec [J. Appl. Cryst. (1995), 28, 289-293] were already obtained by Grimmer in 1979.

Small-angle neutron scattering of precipitates in Ni-rich Ni–Ti alloys. II. Methods for analyzing anisotropic scattering data. Erratum

Correction to J. Appl. Cryst. (1997), 30, 975-985.

AUTO XPL: a Unix shell-script system to sequence X-PLOR refinement runs

A Unix shell script has been written to control the sequential execution of different refinement operations using version 3.851 of Axel Brünger's program X-PLOR.

LAUEGEN version 6.0 and INTLDM

LAUEGEN version 6.0 is an enhanced version of the original X-Windows-based program and now enables the processing of Laue diffraction data up to and including the integration of spot intensities.

SYMMOL: a program to find the maximum symmetry group in an atom cluster, given a prefixed tolerance

A new program to find the maximum symmetry in a molecule or a group of atoms is presented. The symmetrized coordinate and the point-group label and elements are printed out together with some parameters quantifying the deviation from the exact symmetry.

CIF Applications. IX. A new approach for representing and manipulating STAR files

An object-oriented representation of a STAR file with associated applications is presented.

Some diffractometer test crystals: a summary

A summary of many of the test crystals that have been used with single-crystal diffractometers is provided.