Exploratory orientation data analysis with ω sections

Pole point plots are generalized to augmented pole point plots visualizing a second crystallographic direction subjected to random orientations. ω sections of the space of crystallographic orientations generalizing both γ as well as σ sections are introduced into texture analysis and shown to visualize an orientation probability density function more instructively.

Observation of orientational disorder in the hexagonal stuffed tridymite Sr_0.864Eu_0.136Al₂O₄ by the maximum-entropy method

The crystal structure of a strontium europium aluminate, Sr_0.864Eu_0.136Al₂O₄, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method with synchrotron X-ray powder diffraction data. The results suggest that AlO₄ tetrahedra in Sr_0.864Eu_0.136Al₂O₄ are orientationally disordered.

Structure and order in lamellar phases determined by small-angle scattering

Multilamellar phases can be identified and characterized by small-angle scattering of X-rays or neutrons. The recently developed generalized indirect Fourier transformation method is extended to determine simultaneously the structure factor and the model-free form factor.

X-ray diffuse scattering holography

It is shown that anomalous X-ray diffuse scattering can be treated as a hologram providing information on the local environment of the anomalous scatterer.

Study of geometrical local order in a non-ideal solid solution: an intermediary structure

One of the key obstacles in the progress of certain aspects of solid-state physics is the determination of the nature of irregularities in the atomic network of matter and their correlation with macroscopic properties. In this work, an original structural result is presented, namely the presence of icosahedral clusters in an Al solid solution, as deduced from the analysis of the total Fourier-space image.

Powder pattern indexing with the dichotomy method

A new computer program, DICVOL04, based on the successive dichotomy algorithm for powder diffraction pattern indexing is described. Many tests have revealed a high success rate.

Characterization and modelling of germanium assembled crystals for the diffraction of thermal neutrons

Two assembled germanium crystals, produced for use as neutron monochromators, are characterized by means of neutron and X-ray diffraction. The neutron and synchrotron experimental data (reflectivity profiles and topographs) are compared with calculations based on analytical models and Monte Carlo simulations.

Full-profile refinement by derivative difference minimization

A new method of full-profile refinement is developed on the basis of a derivative difference minimization. The method allows powder diffraction structure analysis independently of the background and may also be applicable in many other areas.

Small-angle scattering from spherical core–shell particles: an analytical scattering function for particles with Schulz–Flory size distribution

The scattering function for spherical core–shell particles with a Schulz–Flory size distribution is derived. The analytical solution is applied to describe the small-angle scattering from core–shell systems with different particle size, polydispersity and ratio of core to shell radii.

X-ray imaging with ultra-small-angle X-ray scattering as a contrast mechanism

A new transmission X-ray imaging technique using ultra-small-angle X-ray scattering (USAXS) as a contrast mechanism is described. USAXS imaging is complementary to USAXS and can provide quantitative and qualitative three-dimensional information on the sizes, shapes and spatial arrangements of the scattering objects.

Ab initio structure determination of the Γ form of D-sorbitol (D-glucitol) by powder synchrotron X-ray diffraction

The crystal structure of the Γ form of D-sorbitol [C₆H₁₄O₆, P2₁2₁2, Z = 12, Z′ = 3, a = 24.3012 (2), b = 20.5726 (2), c = 4.8672 (1) Å, V = 2433.30 (3) ų] has been solved ab initio at 293 K from powder synchrotron X-ray diffraction data. A real-space method (Monte-Carlo simulated annealing), followed by Rietveld refinements with geometric soft restraints, has been used.

Lattice strain effects in the measurement of the Si lattice parameter by Laue-case double-crystal diffractometry

The paper examines analytically and numerically the influence of a constant strain gradient on the rocking-curve peak location in a Laue-case double-crystal diffractometer.

Convergent-beam neutron crystallography

The convergent-beam method for time-of-flight neutron crystallography using capillary optics can give expected integrated intensity gains of ∼100 for a Bragg peak for samples as small as the focal spot (∼100 µm). The diffracted beam intensities have expected gains greater than 500 for powder samples of similar dimensions.

Performance of a new furnace for high-resolution synchrotron powder diffraction up to 1900 K: application to determine electron density distribution of the cubic CaTiO₃ perovskite at 1674 K

For accurate crystal structure analysis, a new electric furnace for the measurement of high-resolution (δd/d = 0.03%) synchrotron radiation powder diffraction profiles from materials at high temperatures (up to 1900 K in air) has been designed and fabricated. The electron density distribution of cubic CaTiO₃ perovskite at 1674 K indicates a covalent bond between Ti and O atoms.

About the efficiency of the early FOMs in ab initio protein phasing

Several early figures of merit (FOMs) are tested for their ability to speed up ab initio protein phasing. A new combined FOM is proposed.

Disordered quasicrystals: diffuse scattering in decagonal Al–Ni–Fe

Interpretation of diffuse scattering of decagonal Al–Ni–Co is presented, based on thermal diffuse scattering and Huang diffuse scattering contributions.

Energetic materials: variable-temperature crystal structures of γ- and ∊-HNIW polymorphs

Temperature-dependent (in the range 100–298 K) changes of the crystal lattices of γ- and ∊-hexanitrohexaazaisowurtzitane have been evaluated from the second-rank thermal expansion tensors. Both lattices undergo anisotropic thermal expansion, that of γ-HNIW being more anisotropic than that of the ∊ phase.

Interpretation of small-angle scattering data of inhomogeneous ellipsoids

The parameters that can be obtained by indirect Fourier transformation of small-angle scattering data of inhomogeneous ellipsoids are discussed. Application of this method to experimental SAXS and SANS data is described.

Contribution of powder diffraction for structure refinements of aperiodic misfit cobalt oxides

Misfit cobalt oxide phases Ca₃Co₄O₉ and Ca_0.82(Cu_0.65Co_0.35O₂) have been reinvestigated by Rietveld structure refinements using neutron and synchrotron diffraction data and new insights are given for these complex structures.

HELIX: a helical diffraction simulation program

The program HELIX has been devised as a simple aid to understanding the origin and appearance of fibre diffraction patterns from helical structures.

Re-thinking the role of the beamstop at a synchrotron-based protein crystallography beamline

A 1 mm vertical-profile X-ray beamstop has been designed to operate in the energy range 6–20 keV. The relationship between the beamstop-to-sample distance and air scatter is discussed with the intent of establishing criteria for optimal beamstop positioning during an experiment.

X-ray diffuser

An X-ray diffuser which causes broadening of the synchrotron beam divergence has been developed and used successfully by inserting an amorphous boron powder plate.

HKL2MAP: a graphical user interface for macromolecular phasing with SHELX programs

To simplify the use of the SHELX programs for phasing and as a teaching tool, a graphical user interface, HKL2MAP has been developed.

X-ray scattering from semiconductors

Epitaxy. Physical principles and technical implementation

Forthcoming meetings and short courses