Journal of Applied Crystallography最新文献

The MATTS (multipolar atom types from theory and statistical clustering) data bank is an advanced tool for crystal structure refinement and properties analysis. It applies a multipole model (MM), which describes the asphericity of the atomic electron density and helps to interpret X-ray or electron diffraction data better than approaches based on the spherical atoms approximation. The generation of MATTS data involves density functional theory calculations, and until recently we used the B3LYP/6-31G** level of theory for this stage. However, it was not so clear how the wavefunction level of theory, especially the basis set used, influenced the resulting MM. This study investigates the influence of the wavefunction basis set on the resulting MM from a charge density point of view. For this purpose, we used charge density related properties, such as correlation of electrostatic potentials, atomic electron populations and average electrostatic potential values. The complex analysis reveals that, within the framework of MATTS data generation, the size of the basis set used has the most significant impact on the MM's charge density quality, and switching from double- to triple-zeta basis sets helps notably improve the charge density related properties. This research sets the foundation for the creation of a new version of the MATTS data bank, which will be expanded to include atom types for elements heavier than Kr and selected metal complexes important for biological systems.

An erroneous equation and some values of related parameters in the paper by Toraya [J. Appl. Cryst. (2023), 56, 1751–1763] are corrected.

An erroneous equation and some values of related parameters in the paper by Toraya [J. Appl. Cryst. (2024), 57, 1115–1126] are corrected.

We investigated the position and time dependence of a mechanochemical reaction induced by ball milling using in situ synchrotron powder X-ray diffraction with changing X-ray irradiation position. The mechanochemical reduction of AgCl with Cu was monitored in situ with the X-rays incident at two different vertical positions on the jar. Our previously developed multi-distance Rietveld method was applied to analyze the in situ diffraction data with a 1 min resolution. Both the vertical and the horizontal sample positions were determined using the sample-to-detector distances from the in situ data. Position dependence was found in the powder spreading and induction time. We reveal that the increase rate of the product is independent of the sample position when measured with a 1 min time resolution, confirming the validity of in situ monitoring of part of the space in a milling jar for a gradual mechanochemical reaction.

The continued advancement of complex materials often requires a deeper understanding of the structure–function relationship across many length scales, which quickly becomes an arduous task when multiple measurements are required to characterize hierarchical and inherently heterogeneous materials. Therefore, there are benefits in the simultaneous characterization of multiple length scales. At the National Institute of Standards and Technology, a new neutron far-field interferometer is under development that aims to enable a multi-scale measurement combining the best of small-angle neutron scattering (SANS) and neutron imaging and tomography. Spatially resolved structural information on the same length scales as SANS (0.001–1 µm) and ultra-small-angle neutron scattering (USANS, 0.1–10 µm) will be collected via dark-field imaging simultaneously with regular attenuation radiography (>10 µm). The dark field is analogous to the polarization loss measured in spin-echo SANS (SESANS) and is related to isotropic SANS through a Hankel transform. Therefore, we use this close relationship and analyze results from SANS, USANS, SESANS and dark-field imaging of monodisperse spheres as a validation metric for the interferometry measurements. The results also highlight the strengths and weaknesses of these neutron techniques for both steady-state and pulsed neutron sources. Finally, we present an example of the value added by the spatial resolution enabled by dark-field imaging in the study of more complex heterogeneous materials. This information would otherwise be lost in other small-angle scattering measurements averaged over the sample.

Painted artworks represent a significant group of cultural heritage artifacts, which are primarily admired because of their aesthetic quality. Nevertheless, the value of each particular painting depends also on what is known about it. Material investigation of paintings is one of the most reliable sources of information. Materials in painted artworks (i.e. panel, easel and miniature paintings, wall paintings, polychromed sculptures etc.) represent an extensive set of inorganic and organic phases, which are often present in complicated mixtures and exhibit characteristics reflecting their geological genesis (mineral pigments), manufacturing technology (artificial pigments), diverse biological nature (binders or dyes) or secondary changes (degradation or intentional later interventions). The analyses of paintings are often made challenging by the heterogeneous nature and minute size of micro-samples or, in some cases, even by the impossibility of sampling due to the preciousness, fragility or small dimensions of the artwork. This review demonstrates the successful implementation of laboratory X-ray powder micro-diffraction for material investigation of paintings, illustrating its efficiency for mineralogical analysis of (i) earth-based materials indicating the provenance of paintings, (ii) copper-based pigments pointing to their origin, and (iii) products of both salt corrosion and saponification enabling one to reveal the deterioration and probable original appearance of artworks.