The revenge of the Patterson methods. II. Substructure applications

The efficiencies of Patterson and direct-methods techniques for substructure applications are compared.

Small-angle energy-dispersive X-ray scattering using a laboratory-based diffractometer with a conventional source

Energy-dispersive small-angle X-ray scattering experiments on protein solutions, micelles, semicrystalline polymers and metal oxides are discussed to illustrate the limits and the potentialities of this technique.

Accurate determination and correction of the lattice parameter of LaB₆ (standard reference material 660) relative to that of Si (640b)

X-ray powder diffraction and synchrotron radiation have been used to determine the lattice parameter of the NIST standard reference material (SRM 660) LaB₆ as 4.156468 Å with an accuracy of 12 parts per million (p.p.m.), calibrated relative to the lattice parameter of the Si powder standard [a₀ = 5.430940 (11) Å, Si 640b]. A discrepancy of 0.00048 (5) Å, or nine standard deviations from the NIST reference, is observed between the currently accepted lattice spacing of LaB₆ and the measured value.

Enantiomorph identification of crystals belonging to the point groups 321 and 312 by convergent-beam electron diffraction

Asymmetry in the intensity of the reflections of Bijvoet pairs in a symmetrical zone axis is compared with that of a computer-simulated CBED pattern. The method has been successfully applied to crystals belonging to the point groups 321 and 312.

Small-angle neutron scattering resolution with refractive optics

The resolution of small-angle neutron scattering instruments is investigated for the case where refractive optics (lenses or prisms) are used. The appropriate equations are derived to describe the position and the spatial variance of the neutron beam at the detector in the horizontal and vertical directions, and the minimum value of the scattering vector.

Microstructural evolution of mullites produced from single-phase gels

The crystalline microstructure of mullites, produced by heating monophasic gels, prepared from mixtures of aluminium nitrate and tetraethylorthosilicate, at different final treatment temperatures, is characterized by prevalent crystallite shape, volume-weighted crystallite size distribution and second-order crystalline lattice strain distribution determined from X-ray diffraction patterns. These characteristics, being dependent on process temperature and initial gel chemical composition, are in good agreement with images obtained from field emission scanning electron microscopy and transmission electron microscopy.

Twin structure in the crystallite aggregation pattern

The anisotropy of the NH₄Cl crystallite zigzag aggregation pattern is a twin structure of 6mm symmetry, related to the crystal point group m3m. The twin axis is [110], the twin plane is {211} and the contact interface is {411}.

Small-angle scattering from three-phase samples: application to coal undergoing an extraction process

After deriving the linear relations among the scattering intensities of samples related by slight modifications, we characterize the fluid extraction process of coal.

Phasing of resonant anomalous X-ray reflectivity spectra and direct Fourier synthesis of element-specific partial structures at buried interfaces

A model-independent formalism to obtain element-specific partial structures at buried interfaces using resonant anomalous X-ray scattering is described. The amplitude and phase of an element-specific partial structure factor, obtained with resonant anomalous X-ray reflectivity spectra, allow unknown element-specific partial density distributions at an interface having an arbitrary shape to be reconstructed by discrete Fourier synthesis.

Small-angle scattering analysis of the spherical half-shell

The small-angle scattering structure functions of the single spherical half-shell (SHS) are discussed based on the chord length distribution of the so-called cap chords of a solid hemisphere. Using simple analytic expressions, it is possible to describe the scattering of polydisperse arrangements of non-interacting SHSs.

Nondestructive qu­antitative synchrotron grazing incidence X-ray scattering analysis of cylindrical nanostructures in supported thin films

This paper demonstrates a quantitative, nondestructive analysis of nanostructured thin films supported on substrates and their templated nanopores with grazing incidence X-ray scattering.

A stochastic algorithm for reconstruction of grain maps of moderately deformed specimens based on X-ray diffraction

A stochastic algorithm is presented for the reconstruction of two-dimensional grain maps of embedded layers in moderately deformed polycrystalline specimens based on X-ray diffraction.

Diffraction profiles of elastically bent single crystals with constant strain gradients

Exact and approximate equations are derived which can be used to simulate dynamical scattering artifacts (mirage peaks) that are observed in diffraction from strained single crystals.

High-temperature (1500 K) reciprocal space mapping on a laboratory X-ray diffractometer

A laboratory X-ray diffractometer devoted to the in situ characterization of the microstructure of epitaxic thin films at temperatures up to 1500 K has been built. A specific stage for the in situ correction of the sample holder dilation allows accurate sample positioning over the whole temperature range explored.

Determination by high-resolution X-ray diffraction of shape, size and lateral separation of buried empty channels in silicon-on-nothing architectures

By analysis of transverse and longitudinal scans in the reciprocal space, both crossing a selected reciprocal lattice point, the shape, size and lateral gap of empty channels, distributed as a one-dimensional periodic array below the surface of silicon-on-nothing architectures, were determined thanks to the high-resolution optics adopted for the measurements.

Direct methods and the solution of organic structures from powder data

A procedure is described aiming at recovering a complete crystal structure from a uninterpretable electron density map produced by application of direct methods to powder data.

The healing process for fractured tibia bones of sheep studied by neutron diffraction

The orientation of the mineral crystals of a fractured tibia bone of a sheep is not restored after almost two years of recovery.

Structure and microstructure evolution during martensitic transformation in wrought Fe–26Mn–0.14C austenitic steel: an effect of cooling rate

Rietveld analysis of the X-ray diffraction pattern and electron back-scattered diffraction studies are presented for the structure and microstructure evolution during γ_fcc → ∊_hcp martensitic transformation due to various cooling conditions of wrought austenitic steel.

Anisotropic microstrain broadening due to field-tensor distributions

The anisotropic microstrain distribution resulting from an isotropic distribution of a field tensor (rank 0 or 2), the latter being connected with strain by an anisotropic property tensor (rank 2 or 4), is analyzed. The treatment simplifies the search for a possible physical origin of experimentally observed anisotropic microstrain broadening.

On the entropy to texture index relationship in qu­antitative texture analysis

A sharp inequality is proved between the -norm and the entropy of probability density functions; this inequality is applied to texture analysis by characterizing the relationship between the entropy and the texture index of an orientation density function. The relationship is empirically verified with simulated and experimental data.

X-ray bright-field imaging analyzes crystalline quality and defects of SiC wafers

An extension of the recently developed X-ray bright-field imaging technique is presented that allows the quantitative analysis of crystalline quality parameters such as the lattice plane curvature and the mosaic distribution in SiC wafers.

A new method for the reproducible generation of polymorphs: two forms of sulindac with very different solubilities

A new method for the reproducible generation of polymorphs, `potentiometric cycling for polymorph creation (PC)²', is described. This new method has been applied to sulindac, a non-steroidal anti-inflammatory drug, which also shows promise in anticancer treatment, producing two polymorphs of this API, including a new more stable one.

From CIF to virtual morphology using the WinXMorph program

Crystal morphologies are predicted from data stored in files in CIF format on the basis of the Bravais–Friedel, Donnay–Harker model.

The Fortran90 source of the program PSILAM

The Fortran90 source code of the program PSILAM has been deposited with the IUCr.

A parallel program using SHELXD for quick heavy-atom partial structural solution on high-performance computers

Based on a parallel algorithm designed for SHELXD to solve the heavy-atom partial structures of protein crystals quickly, a program has been developed to run on high-performance multiple-CPU Linux PCs, workstations or clusters.

Crystallization shelf

A model of an air cooler in a laboratory furnace, for simultaneous regulation of different crystallization fronts and rates in crucible columns, with the purpose of obtaining crystals, is presented.

Likelihood of crystallization: experimental and computational approaches

A report on the VIZIER Workshop on the `Definition of protein domains and their likelihood of crystallization', Vienna, Austria, 28–30 June 2006.

Forthcoming meetings and short courses