Laboratory X‐ray powder micro‐diffraction in the research of painted artworksŠvarcová, Silvie; Bezdička, Petr; Hradilová, Janka; Hradil, David
doi: 10.1107/s1600576724008975pmid: N/A
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.
Sheet‐on‐sheet fixed target data collection devices for serial crystallography at synchrotron and XFEL sourcesDoak, R. Bruce; Shoeman, Robert L.; Gorel, Alexander; Niziński, Stanisław; Barends, Thomas R.M.; Schlichting, Ilme
doi: 10.1107/s1600576724008914pmid: 39628875
Serial crystallography (SX) efficiently distributes over many crystals the radiation dose absorbed during diffraction data acquisition, enabling structure determination of samples at ambient temperature. SX relies on the rapid and reliable replacement of X‐ray‐exposed crystals with fresh crystals at a rate commensurate with the data acquisition rate. `Solid supports', also known as `fixed targets' or `chips', offer one approach. These are microscopically thin solid panes into or onto which crystals are deposited to be individually interrogated by an X‐ray beam. Solid supports are generally patterned using photolithography methods to produce a regular array of features that trap single crystals. A simpler and less expensive alternative is to merely sandwich the microcrystals between two unpatterned X‐ray‐transparent polymer sheets. Known as sheet‐on‐sheet (SOS) chips, these offer significantly more versatility. SOS chips place no constraint on the size or size distribution of the microcrystals or their growth conditions. Crystals ranging from true nanocrystals up to microcrystals can be investigated, as can crystals grown in media ranging from low viscosity (aqueous solution) up to high viscosity (such as lipidic cubic phase). Here, we describe our two SOS devices. The first is a compact and lightweight version designed specifically for synchrotron use. It incorporates a standard SPINE‐type magnetic base for mounting on a conventional macromolecular crystallography goniometer. The second and larger chip is intended for both X‐ray free‐electron laser and synchrotron use and is fully compatible with the fast‐scanning XY‐raster stages developed for data collection with patterned chips.
Duality of spaces and the origin of integral reflection conditionsNespolo, Massimo
doi: 10.1107/s1600576724008367pmid: N/A
The dualism between direct and reciprocal space is at the origin of well known relations between basis vectors in the two spaces. It is shown that when a coordinate system corresponding to a non‐primitive unit cell is adopted, this dualism has to be handled with care. In particular, the reciprocal of a non‐primitive unit cell is not a unit cell but a region in reciprocal space that does not represent a unit of repetition by translation. The basis vectors do not correspond to reciprocal‐space cell lengths, contrary to what is stated even in the core CIF dictionary. The corresponding unit cell is a multiple of this region. The broken correspondence between basis vectors and unit cell is at the origin of the integral reflection conditions.
Understanding secondary order parameters in perovskites with tilted octahedraTrotsenko, Ekaterina G.; Talanov, Mikhail V.
doi: 10.1107/s1600576724009397pmid: N/A
In the family of perovskite materials, the tilts of BX6 octahedra are the most common type of structural distortion. Conventionally, the formation of low‐symmetry perovskite phases with tilted octahedra is analyzed by considering only primary order parameters. However, octahedral tilting also gives rise to secondary order parameters which contribute to additional atomic displacements, ordering and lattice distortions. Our study highlights the significant impact of secondary order parameters on the structural formation and emergent physical properties of perovskites. Through group‐theoretical and crystallographic analyses, we have identified all secondary order parameters within Glazer‐type tilt systems and clarified their physical manifestations. We explore the fundamental symmetry relationships among various structural degrees of freedom in perovskites, including tilt‐induced ferroelasticity, correlations between displacements and ordering of atoms occupying different positions, and the potential for rigid unit rotations and unconventional octahedral tilts. Particular emphasis is placed on the emergence of secondary order parameters and their coupling with primary order parameters, as well as their symmetry‐based hierarchy, illustrated through a modified Bärnighausen tree. We applied our theoretical insights to elucidate phase transitions in well known perovskites such as CaTiO3 and RMnO3 (where R = La and lanthanide ions), thereby demonstrating the significant influence of secondary order parameters on crystal structure formation. Our results serve as a symmetry‐based guide for the design, identification and structural characterization of perovskites with tilted octahedra, and for understanding tilt‐induced physical properties.
Optimizing crucible geometry to improve the quality of AlN crystals by the physical vapor transport methodCao, Wenhao; Wang, Shouzhi; Yu, Ruixian; Li, Qiubo; Wang, Guodong; Zhu, Yajun; Wu, Yuzhu; Lv, Lingshuang; Liu, Jingliang; Xu, Xiangang; Zhang, Lei
doi: 10.1107/s1600576724009087pmid: N/A
In the conventional crucible structure for AlN crystal growth by physical vapor transport, owing to the long molecular transport path of Al vapor and the disruption of the gas flow by the presence of a deflector, the Al vapor easily forms polycrystals in the growth domain. The result is increased internal stress in the crystals and increased difficulty in growing large‐sized crystals. On this basis, with the help of finite element simulations, a novel crucible structure is designed. This crucible not only optimizes the gas transport but also increases the radial gradient of the AlN crystal surface, making the enhanced growth rate in the central region more obvious. The thermal stresses between the deflector and the crystal are also reduced. High‐quality AlN crystals with an FWHM of 79 arcsec were successfully grown with this structure, verifying the accuracy of finite element simulation of the growth of AlN crystals. Our work has important guiding significance for the growth of high‐quality AlN crystals.
The smearing function for a multi‐slit very small angle neutron scattering instrumentHan, Zehua; Ma, Changli; Zhu, Hong; Cui, Tengfei; Zuo, Taisen; Cheng, He
doi: 10.1107/s1600576724009014pmid: N/A
Besides traditional pinhole geometry, the multi‐slit very small angle neutron scattering instrument (MS‐VSANS) at the China Spallation Neutron Source also utilizes a multi‐slit collimation system to focus neutrons. Using the special focusing structures, the minimum scattering vector magnitude (q) can reach 0.00028 Å−1. The special structures also lead to a significantly different smearing function. By comparing the results of theoretical calculations with experimental data, we have validated the feasibility of a smearing method based on a mature theory for slit smearing. We use the weight‐averaged intensity of neutron wavelength as a representative to evaluate the effect from a broad wavelength distribution, concentrating on the effect from the geometry of the multi‐slit structures and the detector. The consistency of the theoretical calculation of the smearing function with experimental VSANS scattering profiles for a series of polystyrene standards of different diameters proves the feasibility of the smearing method. This marks the inaugural use of real experimental data from an instrument employing a multi‐slit collimation system.
Integrating machine learning interatomic potentials with hybrid reverse Monte Carlo structure refinements in RMCProfileCuillier, Paul; Tucker, Matthew G.; Zhang, Yuanpeng
doi: 10.1107/s1600576724009282pmid: 39628890
Structure refinement with reverse Monte Carlo (RMC) is a powerful tool for interpreting experimental diffraction data. To ensure that the under‐constrained RMC algorithm yields reasonable results, the hybrid RMC approach applies interatomic potentials to obtain solutions that are both physically sensible and in agreement with experiment. To expand the range of materials that can be studied with hybrid RMC, we have implemented a new interatomic potential constraint in RMCProfile that grants flexibility to apply potentials supported by the Large‐scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) molecular dynamics code. This includes machine learning interatomic potentials, which provide a pathway to applying hybrid RMC to materials without currently available interatomic potentials. To this end, we present a methodology to use RMC to train machine learning interatomic potentials for hybrid RMC applications.
Mapping domain structures near a grain boundary in a lead zirconate titanate ferroelectric film using X‐ray nanodiffractionUdovenko, Stanislav; Son, Yeongwoo; Tipsawat, Pannawit; Knox, Reilly J.; Hruszkewycz, Stephan O.; Yan, Hanfei; Huang, Xiaojing; Pattammattel, Ajith; Zajac, Marc; Cha, Wonsuk; Pagan, Darren C.; Trolier-McKinstry, Susan
doi: 10.1107/s1600576724009026pmid: 39628888
The effect of an electric field on local domain structure near a 24° tilt grain boundary in a 200 nm‐thick Pb(Zr0.2Ti0.8)O3 bi‐crystal ferroelectric film was probed using synchrotron nanodiffraction. The bi‐crystal film was grown epitaxially on SrRuO3‐coated (001) SrTiO3 24° tilt bi‐crystal substrates. From the nanodiffraction data, real‐space maps of the ferroelectric domain structure around the grain boundary prior to and during application of a 200 kV cm−1 electric field were reconstructed. In the vicinity of the tilt grain boundary, the distributions of densities of c‐type tetragonal domains with the c axis aligned with the film normal were calculated on the basis of diffracted intensity ratios of c‐ and a‐type domains and reference powder diffraction data. Diffracted intensity was averaged along the grain boundary, and it was shown that the density of c‐type tetragonal domains dropped to ∼50% of that of the bulk of the film over a range ±150 nm from the grain boundary. This work complements previous results acquired by band excitation piezoresponse force microscopy, suggesting that reduced nonlinear piezoelectric response around grain boundaries may be related to the change in domain structure, as well as to the possibility of increased pinning of domain wall motion. The implications of the results and analysis in terms of understanding the role of grain boundaries in affecting the nonlinear piezoelectric and dielectric responses of ferroelectric materials are discussed.