Electric properties of KTiOPO₄ and NaTiOPO₄ from temperature-dependent X-ray diffraction

The origins of pyroelectricity and ionic conductivity on an atomic scale are described using results from accurate X-ray diffraction analyses, at several temperatures, of the electron-density distribution.

Geometric distortion corrections for fiber-optic tapers in X-ray charge-coupled-device detectors

A simple algorithm is proposed for quantifying and correcting geometric distortions introduced by fiber-optic tapers in an X-ray CCD detector with direct taper coupling.

Crystal structures of a solvated and unsolvated sulfone cyclic oligomer

The conformation of the macrocyclic [2+2] dimer formed from 4,4′-dichlorodiphenyl sulfone and bisphenol-A has been determined in the unsolvated material and in the dimethyl sulfoxide solvate. Intermolecular phenyl–plenyl stacking interactions are apparently important in determining the conformation in the solid state.

Restitution conditions of the parent cubic texture from the inherited hexagonal texture in the β–α phase transformation

The conditions for calculating the parent texture from the inherited texture in the β–α transformation are discussed. The use of a specific correlation function allows information to be gained in the case of variant selection.

X-ray diffraction study of concentration depth profiles of binary alloy coatings during thermal diffusion: application to brass coating

Using the Houska method based on X-ray diffraction-line profile analysis, new mathematical treatments are proposed to compute the concentration depth profile of thin films obtained by diffusion. Concentration depth profiles of a brass layer are reported.

Rietveld refinement guidelines

A set of general guidelines for structure refinement using the Rietveld (whole-profile) method has been formulated by the IUCr Commission on Powder Diffraction. The practical rather than the theoretical aspects are discussed.

Rietveld refinement of site-occupancy parameters of Mg_2−xMn_xSiO₄ using a new weight function in least-squares fitting

A new weight function for the minimization function used in the Rietveld method has been applied to the determination of site occupancy under various refinement conditions. The accuracy of refined site-occupancy parameters of Mg_2−xMn_xSiO₄ was comparable to that obtained in single-crystal studies.

Structural characterization of free-standing gallium arsenide coiled membranes produced by micromachining

High-resolution X-ray diffraction study of coiled membrane sensors has revealed in-built stresses, manifested as tilts between different segments of the sensor, and the morphology of the cavity below the membrane. The degree of crystalline perfection of the membrane has been determined.

Calibration of spiral-readout image-plate detectors

An improved method of calibrating disk-like image-plate systems is shown to dramatically reduce systematic errors in structure factors and refined protein models.

Small-angle X-ray scattering analysis of craze-fibril structures

Three variations of the Porod-law model have been applied to the small-angle scattering from craze-fibril structures. It was determined that the sigmoidal-gradient model of diffuse boundaries provides the best description of these oriented rod-like structures.

Laser-induced transient structure and stress in a platinum(111) crystal studied by time-resolved X-ray diffraction

Nanosecond time-resolved X-ray diffraction measurements of Pt(111) transient lattice spacing induced by laser heating are described.

A tangent formula derived from Patterson-function arguments. VI. structure solution from powder patterns with systematic overlap

The direct methods sum function is adapted to cope with data from powder patterns with systematic overlap. In contrast to usual two-stage procedures, both multiplet decomposition and phase refinement are carried out simultaneously.

Implementation of a six-dimensional search using the AMoRe translation function for difficult molecular-replacement problems

A six-dimensional molecular-replacement search has been implemented using Perl scripts to drive the AMoRe translation function and to analyze the results.

Use of cryoprotectants in combination with immiscible oils for flash cooling macromolecular crystals

The high concentration of cryoprotectant needed to prevent ice formation during cooling to cryogenic temperatures sometimes damages the fragile crystals it is supposed to protect. The described combination procedure permits the successful flash cooling at greatly reduced concentration of cryoprotectant.

A gentle vapor-diffusion technique for cross-linking of protein crystals for cryocrystallography

A new method for glutaraldehyde cross-linking of protein crystals is presented. The introduction of intermolecular cross-links serves to prevent lattice disorder of fragile crystals during rapid-cooling procedures.

Isotope effects in solution small-angle X-ray scattering

The importance of recognizing the difference between H₂O and D₂O solvents for SAXS is discussed.

SIR97: a new tool for crystal structure determination and refinement

The program SIR97 is a versatile tool for direct solution and complete refinement of crystal structures.

The design and implementation of SnB version 2.0

A new version (v2.0) of the direct-methods program SnB is described. SnB v2.0 has been successfully applied to a structure containing 1000 unique non-H atoms and a Se substructure with 30 anomalous sites.

CIF Applications. XI. A La Mode: a ligand and monomer object data environment. I. Automated construction of mmCIF monomer and ligand models

A new ligand and monomer object data environment named A La Mode is described for building chemical-component models in the mmCIF representation from surveys of high-resolution small-molecule crystal structures. Examples of the application of this system are presented for an intercalating drug component and for a nucleotide unit constructed from independent base, sugar and phosphate constituents.

Condensation-free X-ray diffraction data collection with capillaries at 277 K

Sealing with oil plugs was used as a means to prevent condensation problems in the collection of X-ray diffraction data at 277 K with capillaries cooled by a gas stream from a cryocooler.

Notes for Authors 1999