Crystallography Reports最新文献

The disadvantages of the “strategy” scan-lists for diffraction experiments, created by the diffractometer software, are shown. The reason for these disadvantages is that the traditionally used goal function solves a limited, local meaning, for example, to obtain the best coverage of the reciprocal space. An approach is proposed that implements the principles of statistical randomization of the experiment and allows achieving the strategic goal of structural analysis: obtaining a model capable of reflecting the subtle details of the atomic structure. A scan-list balanced by most factors has been found, which in less time leads to obtaining experimental data of much higher quality than traditional lists. The use of a reference crystal, previously measured dozens of times on diffractometers around the world, has shown the advantage of the experimental data obtained by the new method. Increasing the balance and accuracy of the data resulted in maximum improvement of the values of the refinement criteria: to R1/wR2 = 0.53/0.59% and Δρ = –0.47/+0.30 e/ų. The achievement of the strategic goal of the research of the reference crystal (confirmation of the anharmonic model of atomic displacement parameters) could be confirmed not only by the purification of the difference Fourier syntheses of electron density, which is sometimes visual and subjective, but also by a statistically flawless decrease in the R factors of refinement by 30–40 rel %. Data of such high quality are needed to study the dynamics of structural models under external conditions, for the detection and modeling of phase transitions, critical points, bio- and chemical activity of compounds, verification of computational structural methods.

A specialized experimental setup has been designed and manufactured for X-ray diffraction studies under external magnetic fields on the sample. The setup includes a set of precision automated electromechanical drives, which enable orientation of the permanent magnet-based magnetic system along various crystallographic directions of the studied sample. The system provides automated variation in the strength and direction of external magnetic field during the experiment. The setup is compatible with blower-type heating attachments, allowing for research in a wide temperature range. The specified performance of the setup and its high parameter stability have been validated through a series of experiments on X-ray scattering near absorption edges using iron borate single crystals.

The results of studying two ⁶LiInSe₂ single crystals using highly enriched ⁶Li isotope are presented. The interaction of neutrons with crystals has been calculated with the aid of the Geant4 toolkit, theoretical values of the detection efficiency were obtained, and a comparison with a ³He detector was carried out. The possibility of separating neutrons and gamma quanta by the pulse-shape discrimination method is considered.

The possibilities of a complex study of the 3D structure of a polymeric spongy matrix based on polylactide, using X-ray microtomography without staining in combination with noninvasive method scanning impulse acoustic microscopy and energy-dispersive X-ray microanalysis, are presented. Comparative studies of pure matrix samples, in vitro samples kept in a culture medium and after their implantation in vivo were carried out. The use of a complex of noninvasive methods revealed changes in the microstructure, including matrix degradation processes in a culture medium, after incubation with cells and implantation in a laboratory animal.

The dependence of the solubility of Ni_xCo(_{{1-x}})SO₄⋅6H₂O (x = 0–1) on the composition of the solution at a temperature of 45°C has been obtained. It is found that heating leads to a shift of the point of invariant equilibrium of the tetragonal and monoclinic phases towards a higher cobalt concentration in the solution. A thermogravimetric study showed that the thermal stability of the crystal decreases with an increase in the Co content in it. The spectral characteristics of crystals of different compositions showed that the crystal under study can be used as a UV filter. The habit of a monoclinic Ni_xCo(_{{1-x}})SO₄⋅6H₂O crystal, obtained from a solution of the NiSO₄ : CoSO₄ = 50 : 50 wt % composition, was determined.

The results of studying aqueous solutions of guanilurea hydrogen phosphite (GUHP), in particular, the isothermal cut of the phase diagram in the system of initial reagents for the synthesis of GUHP salt at 25 and 45°C, are presented. The solubility of GUHP in water was studied as a function of pH. The conditions for bulk crystal growth are determined. The indexing of GUHP crystal faces was performed. The features of the real structure of GUHP single crystals were studied in dependence of the growth conditions for the first time.

A three-dimensional reconstruction of the microstructure of the defects associated with the formation of fatigue cracks in samples destroyed during low-cycle fatigued tests has been performed by serial-section focused ion beam tomography. The geometric parameters of defects containing Hf, Nb, Ti, Al, and Ni, identified during 3D reconstruction, were determined. The morphology of individual particles is presented by a set of shapes that form flat (carpet-like) conglomerates up to several tens of microns in size, which cannot be detected by nondestructive testing methods. The revealed morphological features make it possible to propose a complex of measures aimed at increasing the service life of parts made of granulated heat-resistant nickel alloy EP741NP; this is an important practical result.

Nanosized polysubstituted solid solutions, containing from three to eight di- and trivalent cations in different quantitative ratios, with the general formula (M_{{1 - x}}^{n}R_{x}^{m}{{{text{F}}}_{{2 + x}}}), where M = Ca, Sr, Ba, Pb, R = La, Gd, Dy, Yb, n = 3 and 4, m = 0, 1, 2, and 4, and х varies from ~0.07 to ~0.3 for different cationic compositions, have been obtained by coprecipitation from aqueous solutions of nitrates. They all retain the fluorite structure (structural type CaF₂, space group (Fmbar {3}m)). The possibilities of precipitation of mixed solid solutions with different combinations of cations and using different fluorinating agents were demonstrated. It is shown that the obtained solid solutions are medium- and high-entropy phases.

Many structural metallic materials (in particular, hafnium, zirconium, and titanium alloys) exploited in hydrogen-containing media tend to form brittle hydride phases when absorbing hydrogen, which deteriorates their mechanical properties. Determination of the terminal solid solubility (the hydrogen concentration in a metal at which hydride formation occurs) is an important and time-consuming experimental task. The purpose of this study is to develop a new approach based on the hydrogen permeation method, which makes it possible to find the terminal solid solubility at isothermal saturation without using an expensive equipment. The technique is based on the change in the character of hydrogen permeation through a membrane from a material studied as a result of the hydride phase formation; this technique imposes certain limitations on the experimental conditions. They are related to the parameters of the surface and bulk processes of hydrogen interaction with the material. The importance of the correct choice of experimental conditions for determining the terminal solid solubility of hydrogen in metals was demonstrated using computer simulation, the possibility of applying the technique to hafnium was analyzed, and the protocol and parameters of the experiment were substantiated.