Том 63, № 4 (2018)

A new approach to numerical simulation of double-crystal rocking curves is proposed. This approach is based on the use of experimental spectral angular diagrams of X-ray intensity distribution. Special calculation algorithms, which take into account the instrumental function of X-ray diffractometer and possible effects of dispersion and Bragg reflection asymmetry, have been developed and applied. A specific feature of the proposed approach is the possibility of visualizing the 2D spectral angular diagram of X-ray beam after its interaction with each element of the scheme. The approach makes it possible to perform calculations for a wide range of radiation sources (from an X-ray tube with any anode to a synchrotron radiation source) and X-ray optical elements (slits and monochromators). A comparison of simulation results and experimental data for a Si(110) crystal sample has confirmed adequacy of the proposed approach and its applicability for simulating diffraction patterns recorded in real experiments.

The results of the first experimental realization of a spectrometer based on the effect of diffraction focusing of X rays by a flat single crystal are discussed. A secondary X-ray source with a relatively high angular divergence and small sizes was formed at the focus of a compound refractive lens having 50 beryllium biconcave elements with a curvature radius of 50 μm. The silicon spectrometer crystal was cut in the form of a wedge of variable thickness, oriented perpendicular to the diffraction plane. The reflection 111 was used for energies of 8.3 and 12 keV. To simulate the experiment, a computer program was developed, which takes into account accurately and for the first time the focusing of radiation by the lens and its subsequent diffraction in the crystal. A calculated curve for a monochromatic beam has made it possible to determine the monochromator spectrum with high resolution from experimental data for a polychromatic beam. It is shown that monochromator resolution increases with an increase in the distance from the compound refractive lens to the crystal.

A geometrical and topological analysis of intermetallic compounds A₂^[16]B₄^[12] of the Friauf families Mg₂Cu₄ (formed in 273 binary and 775 ternary systems) and Mg₂Zn₄ (formed in 67 binary and 121 ternary systems) has been performed. Basic 3D nets are determined in the form of a graph, whose sites correspond to the centers of tetrahedral cluster precursors В₄: Cu-type net with a coordination number (CN) of 12 for Mg₂Cu₄ and a BN-type net with a CN of 8 for Mg₂Zn₄. The symmetry and topology code is determined for the crystal structure self-assembly in the following form: primary chain S₃¹ → microlayer S₃² → microframework S₃³. An identical mechanism of primary chain S₃¹ self-assembly from B₄ clusters with participation of large template atoms A^[16] for both families and a mechanism of S₃² microlayer self-assembly from parallel S₃¹ chains in Mg₂Cu₄ (basic 2D net 4⁴) and shifted chains in Mg₂Zn₄ (basic 2D net 3⁶) have been determined for the first time. The constant chemical composition of intermetallic compounds A₂^[16]B₄^[12] is related to the functional difference between the B atoms forming 3D frameworks and template atoms А. The numbers of chemically different В₄ clusters for the Mg₂Cu₄ and Mg₂Zn₄ families are found to be 25 and 19, respectively.

The structure of (K_1–x(NH₄)_x)₃H(SO₄)₂ crystals with a low ammonium concentration and the behavior of their thermal, optical, and dielectric properties in a temperature range of 275–500 K have been investigated to clarify the influence of doping on the phase transition kinetics. An examination of unit-cell parameters of (K_{1 – x}(NH₄)_x)₃H(SO₄)₂ single crystals has confirmed the existence of a superprotonic phase transition at a temperature of ≈450K. The conducting properties of single-crystal and polycrystalline samples have been studied.

The (NC₅H₂(C₆H₅)₄)₂[Re₂Cl₈] · 2CH₃CN compound was prepared by the reaction of (n-Bu₄N)₂[Re₂Cl₈] with the 1,2,4,6-tetraphenylpyridinium tosylate in the acetonitrile; it crystallizes upon cooling of the solution at –15°C. The structure consists of the ((C₆H₅)₄C₅H₂N)⁺ cation and Re₂Cl₈²⁻ anion with virtual D_4h symmetry. The average Re–Re and Re–Cl bond distances are 2.2205 and 2.3431 Å, respectively. In the structure, the Re₂Cl₈²⁻ anions are disordered, such that 71.34% of the Re–Re units are aligned in one direction while 28.66% are aligned orthogonal to it. The principal crystallographic data are as follows: sp. gr. R̅3; a = 26.554(1) Å, c = 23.666(1) Å; V = 14451.6(1) ų; Z = 9; D_x = 1.643 g cm^–3.

A new coordination polymer, namely, [Cd(L)(BIB)_0.5]_n (H₂L = benzophenone-2,4′-dicarboxylic acid, BIB = 1,4-bis(1H-imidazol-1-yl)butane), was synthesized under hydrothermal condition. Single-crystal X-ray analysis reveals that two adjacent Cd(II) ions are bridged by four L²⁻ ligands to form a two-dimensional layers, which are further connected by BIB to build a beautiful three-dimensional (3D) network. The luminescent and thermal properties of the compound are investigated.

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine, which plays a pivotal role in the regulation of immune response. Hence, the search for new inhibitors of MIF tautomerase activity has attracted great attention. This protein is known to serve as a superligand, by involving in protein–protein interactions that are poorly studied. Macrophage migration inhibitory factor was prepared in complex with albumin, and its solution structure was studied. Difficulties encountered in performing this research were due to the fact that the sample was a mixture of the MIF–albumin complex and the individual proteins. The interaction was found to be weak and unstable. Three most probable models of the MIF–albumin complex were obtained using small-angle X-ray scattering and molecular docking simulation, and one of these models was shown to be preferable. One albumin molecule binds to the MIF trimer in the active-site region of the protein.

A water soluble compound, (2-((1H-benzimidazol-2-yl)methylamino)acetic acid, BIGH, has been synthesized and structurally characterized by elemental analysis, IR and UV spectroscopies, ¹H-NMR, thermogravimetric and differential thermal analyses, and single crystal and powder X-ray diffraction. BIGH can act as a flexible planar ligand with three potential coordination sites. It crystallizes in a monoclinic system with the sp. gr. P2₁/c with the unit cell parameters, a = 9.3764(7) Å, b = 11.5031(8) Å, c = 10.0543(6) Å, and Z = 4. The crystal structure was stabilized through inter-molecular hydrogen bonds. The anti-microbial activity of the compound has been studied against Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus, which showed a good activity against Bacillus subtilis. Cyclic voltammogram of the compound shows that it is a redox-active molecule.

The influence of the imperfection of a polarizer, an analyzer, and a photoelectron multiplier of a spectrophotometric complex on the intensity of light passed through a plane-parallel plate of a uniaxial transparent or absorbing crystal has been theoretically investigated. Expressions for calculating the birefringence and dichroism at different wavelengths are obtained and analyzed. It is established that the influence of the imperfection of optical elements is stronger for calculating the birefringence value, as compared with the calculation of dichroism.

It is shown how the entire energy of an acoustic beam incident on a boundary of a hexagonal crystal can be directed into a narrow reflected beam propagating at a small angle to the surface. This process is accompanied by mode conversion: the incident and reflected beams belong to different acoustic branches. The conversion near the total internal reflection is implemented by matching the orientations of the sagittal plane and surface and thereby eliminating the loss for parasitic wave reflection. The found conversion conditions and resonant reflection parameters are expressed in terms of the moduli of elasticity of crystal.

Waveguide lasing in a layer of nematic liquid crystal (NLC) doped with a dye has been experimentally observed. A chromium micrograting with a period of 1.76 μm has been deposited on the surface one of the cell substrates to provide a distributed feedback (DFB) and partially extract laser radiation to a quartz substrate. The DFB provides lasing in the ninth diffraction order for waveguide TM modes. Laser radiation is observed at the output of the substrate end face at an angle of 67.0° ± 1.5° with respect to the normal to the waveguide plane. An increase in voltage across the micrograting electrodes leads to red-shifted multimode lasing. A numerical simulation of a structure imitating the experimental cell has shown good agreement between the calculation results and experimental data.

Lead zirconate titanate (PZT) films doped with lanthanum, Pb(_1–х)La_х(Zr_0.48Ti_0.52) (х = 0, 0.02, 0.05, 0.08, or 0.01), have been investigated by electron microscopy and X-ray diffraction. Films were formed on Si–SiO₂–TiO₂–Pt substrates by chemical vapor deposition from a solution and annealed at temperatures T = 650 and 750°C. The main structural features of the films, differing them from undoped PZT films fabricated by the same method, have been established. It is found that doping with lanthanum delays the pyrochlore–perovskite transformation in the film bulk, i.e., in the regions distant from the film–substrate interface. The fraction of metastable pyrochlore phase increases with an increase in the La molar content in the films. The main reason for the delay is the deficit of lead in the intergranular perovskite space, especially in the upper part of the film. Annealing at T = 750°C reduces the content of pyrochlore phase but does not completely remove it, which was never observed for undoped PZT films. Doping with lanthanum leads to a change in the lattice period c and a tetragonal distortion of the perovskite lattice (c/a ratio). Hence, the [100] texture of the films obtained, in contrast to the typical [111] texture of PZT films, is due to the increase in the lattice mismatch between the film and platinum layer when lead atoms are replaced with lanthanum. Lattice distortions of “transrotational” character, whose value exceeds 160 deg/μm, are found to arise in growing crystals.

Bicrystal substrates, in which (100) planes in both single-crystal parts are rotated with respect to the surface by different angles around the [100] and [110] directions (parallel simultaneously to both the surface and bicrystal boundary), have been fabricated by solid-phase intergrowth on SrTiO₃ crystals. Epitaxial bicrystal YBa₂Cu₃O₇ films with different tilt angles of CuO planes to the surface have been grown on these bicrystals by pulsed laser deposition. The structure of these films has been investigated by X-ray diffraction. The films are shown to remain epitaxial when the film lattice is rotated from the position in which its (001) plane is oriented parallel to the surface by angles of up to 41° and 49° around the [100] and [110] axes, respectively. The possibility of growing bicrystal films of YBa₂Cu₃O₇ high-temperature superconductor (HTSC), in which the CuO planes at different sides of the bicrystal boundary make different angles (up to 90°, which is the maximum possible angle from the symmetry point of view), has been demonstrated based on these data.

The processes of grinding and transformation of the structure of the ZnO–C powder mixture at the mechanical activation by ball milling in an inert atmosphere have been investigated. The mechanical activation of the ZnO–C powder mixture is shown to lead to the formation of graphene oxide shells on the surface of crushed zinc oxide particles. The influence of the duration of activation of powder mixtures on the dynamics of their compaction during spark plasma sintering and structure of the ceramics obtained has been investigated. It is established that an increase in the activation duration to 100 h leads to a monotonic decrease in the density of sintered ceramics. The carbon shell formed during sintering at ZnO grain boundaries is shown to have the structure of reduced graphene oxide.

Some factors affecting the stability of KH₂РО₄ aqueous solutions have been investigated. The width of the metastable zone of KH₂РО₄ solutions saturated at a temperature of 65–80°C is estimated. The solubility curves of the solutions with pH values of 2.5 and 5.4 are analyzed, and the influence of pH on the stability of KH₂РО₄ solutions in growth crystallizers is investigated for the first time.

A method to fabricate insulator microstructures from aqueous solutions using track membranes as a template has been developed by an example of potassium dihydrogen phosphate. It is shown that microstructures are formed in pores of a track membrane under conditions of forced flow of supersaturated crystallization solution through this membrane. These microstructures continue to grow beyond the pore volume, mainly on the membrane side facing the flow. Their transverse sizes and growth direction are determined by the direction and diameter of membrane pores.

Bronze statues “John the Baptist” and “Dancing Cupid” from the collections of the Pushkin State Museum of Fine Arts have been investigated at the National Research Centre “Kurchatov Institute.” These statues were previously damaged in fire. Before carrying out restoration, it was necessary to perform their complex study, including identification of statue materials; elemental and phase analysis of contaminations; estimation of the state of surfaces and internal parts; and detection of technological elements, as well as hidden defects, corroded parts, and cracks. To this end, scanning electron microscopy with X-ray microanalysis, synchrotron radiation diffraction, and neutron radiography and tomography have been used.

Reference no. 1 should read as follows:

J. H. Burnett, Z. H. Levine, and E. L. Shirley, U.S. Patent No. 7163649 (2007).

Reference no. 3 should read as follows:

R. Yu. Shendrik, E. A. Radzhabov, and A. I. Nepomnyashchikh, Tech. Phys. Lett. 39 (7), 587 (2013).

Reference no. 6 should read as follows:

S. M. Gechev, J. T. Mouhovski, and P. Tzvetkov, Journal of International Scientific Publications: Materials, Methods & Thechnologies 9, 326 (2015).

Reference no. 7 should read as follows:

V. S. Urusov, Yu. P. Grigorash, M. Z. Kazakevich, et al., Geokhimiya, No. 11, 1700 (1980).

Reference no. 13 should read as follows:

B. Kostova, J. Mouchovski, O. Petrov, et al., Mater. Chem. Phys., No. 113, 260 (2009).

Reference no. 22 should read as follows:

V. Dimov, B. Kostova, and L. Konstantinov, J. Optoelectron. Adv. Mater.: Symp. 1 (3), 292 (2009).