Vol 64, No 6 (2019)

The Cayley graphs of crystallographic groups \(G_{p}^{p}\), constructed on the minimal number of generators, are discussed. Some theorems on the existence of minimal nets, homeomorphic to such graphs, are proven. The Cayley graphs of planar and Fedorov groups, related to the arrangement of molecular crystals, are considered in detail.

The layer-by-layer growth of Ammann-Beenker graph (a quasi-periodic graph with eightfold symmetry) has been experimentally and theoretically studied. The limiting form for the growth of Ammann-Beenker graph is established in the form of a regular octagon, whose vertices are found explicitly. The lower and upper bounds of this form, which coincide with the growth form, are proven rigorously.

The microstructure of a cold-rolled tape made of Nb–50 wt % Ti superconducting alloy before and after heat treatment has been investigated by transmission electron microscopy, scanning transmission electron microscopy, and microanalysis (including the mode of in situ annealing in the electron microscope column). The influence of heat treatment on the concentration and lateral sizes of α-Ti particles has been calculated. The Ti phase inclusions with fcc lattice are found in the α-Ti particles after in situ annealing.

The defect structure of as grown single crystals Sr_1 – xSm_xF_2 + x (x = 0.14, 0.26) and Sr_1 – xGd_xF_2 + x (x = 0.12, 0.19, 0.30) grown under identical conditions was studied by X-ray diffraction. All crystals belong to the CaF₂ structure type, sp. gr. \(Fm\bar {3}m\). All phases contain interstitial fluoride ions in the 48i site and vacancies in the main anionic motif. In Sr_0.70Gd_0.30F_2.30 interstitial fluoride anions were found also in the 4b site; in Sr_0.88Gd_0.12F_2.12, in the 32f site. Relaxation displacements of a part of F_(8c) anions to the 32f site are observed in Sr_0.86Sm_0.14F_2.14. Displacements of cations to the 24e site occur in all the phases under study; in the phases with R = Gd, there are also displacements to the 32f site. A model of the defect structure of the phases Sr_1 ‒ xR_xF_2 + x (R = Sm, Gd) is proposed. According to this model, interstitial fluoride anions and R³⁺ cations are grouped into octacubic clusters [Sr_14 – nR_nF_64 + n]. The average number of R³⁺ per cluster decreases from 6 to 4.5 with increasing х, the volume of the cluster core increases from 61.2(1) to 65.9(2) ų, and the volume per cluster decreases from 2419.9(5) to 783.5(2) ų.

Polycrystals of CuGaIn₂Se₅ solid solution have been synthesized for the first time. X-ray diffraction analysis revealed that the sample studied is crystallized in the tetragonal system with the lattice parameters а = 5.6689(2) Å, с = 11.3289(7) Å, V = 364.07(3) ų, sp. gr. I\(\bar {4}\), ρ_x = 5.5838(5) g/cm³, М = 757.706, and R_Bragg = 1.33%. The crystal structure is determined, and the electrical and thermal conductivities are measured.

1,3-Dicarbonyl compounds were synthesized by the reaction of 9,10-phenanthrenequinone with acetylacetone and acetoacetic ester followed by the reduction and were characterized by spectroscopic and quantum-chemical methods. In the crystalline state and in solution, these compounds were found to exist in the keto form. The molecular and crystal structure of the binuclear lantern-type copper(II) carboxylate complex Cu₂[μ₂-OOCCH₂(C₁₄H₈)(CO)₂OC₂H₅]₄(NCCH₃)₂, which was formed through the oxidation of the starting 1,3-dicarbonyl compound upon the complexation, was determined by X-ray diffraction. The coordination polyhedron of each copper atom can be described as a (4 + 1) square pyramid with four O atoms of four carboxyl groups at the base and the acetonitrile N atom in the apical position. The formation of the lantern-type dimer is attributed to the μ₂-O,O' bidentate-bridging coordination mode of carboxyl groups.

The interaction of an aqueous suspension of fine-grained iron with one equivalent of (1-hydroxy-ethylidene)diphosphonic acid (H₄L) leads to the formation of poorly soluble iron(II) (1-hydroxy-ethylidene)diphosphonate (FeH₂L · H₂O), which precipitates from the solution in the form of whiskers. A compound consisting of crystalline and X-ray amorphous fractions, whose structure is based on stacked sheets of whiskers, linked by amorphous phase, was selected from the FeH₂L · H₂O reaction mixture with morpholine. The compounds have been studied by methods of elemental analysis, scanning electron microscopy, optical microscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis.

The double mutant of Wolinella succinogenes L-asparaginase (Was72) with the V23Q and K24T substitutions in the C-terminal region of the N-terminal loop enclosing the active site was crystallized in the apo form and in complexes with L-aspartic and L-glutamic acids. This mutant exhibits glutaminase activity eight times lower compared to the wild-type enzyme. Crystals of the apo enzyme were grown in two modifications (sp. gr. P2₁ and sp. gr. P22₁2₁). Crystals grown in the presence of both aspartic and glutamic acids belong to the same space group (P2₁) but have different unit cell parameters. The X-ray diffraction data sets were collected from all types of crystals at 1.65–2.00 Å resolution. All X-ray diffraction data sets are suitable for the determination of the three-dimensional structure of the enzyme.

Gallstones with a zonal morphological structure have been studied using X-ray microtomography, X-ray diffraction analysis, Raman spectroscopy, and elemental analysis. Concrements have been investigated in vitro in the dried state; phases of cholesterol, bilirubin, calcium carbonate, and sodium and potassium chlorides are found in their composition. The analysis is performed within the development of tomographic methods, which can be used in future for intravital diagnostics of cholesterol cholelithiasis. The possibility of determining the phase composition of heterogeneous gallstones, based on the analysis of linear-absorption-coefficient distributions derived from X-ray monochromatic microtomography data, is demonstrated. The results of the tomographic analysis are in agreement with the data obtained using conventional direct methods for determining the phase and elemental composition of the objects under study.

K₂Ni(SO₄)₂ · 6H₂O (KNSH), K₂Co(SO₄)₂ · 6H₂O (KCSH), and K₂Ni_xCo_(1 – x)(SO₄)₂ · 6H₂O (KCNSH) crystals have been grown by traditional and accelerated techniques. The microhardness and crack lengths were measured by indentation with a Vickers pyramid in dependence of the crystal growth conditions in order to improve the crystal structure and properties. It was shown that, with an increase in the growth rate, the stress intensity factor of the crystals (which characterizes the fracture toughness) changes in dependence of the composition: it decreases for KCSH (due to the rise in inhomogeneity) but increases for KCNSH, which is explained by lowering the level of both the mosaic and radial inhomogeneity. In the case of KNSH crystals, the fracture toughness of the {110} sector decreases, whereas the changes in the sector {001} of “slow” crystal are differently directed, which is explained by the high inhomogeneity of its composition.

An X-ray diffraction study of the atomic structure of paratellurite (α-TeO₂) crystal in the temperature range of 86–500 K has been performed. Regions of atomic electron density, shaped as helices with axes oriented parallel and perpendicular to the optical axis, are selected; these regions are found to be the structural basis of the optical activity of crystal. All helices turned out to be right-handed. The values of optical rotation in the directions parallel and perpendicular to the optical axis have been calculated using structural data. These values have identical signs, as was suggested proceeding from the identical twist of electron density helices.

The anomalous plastic creep of sapphire crystals in the temperature range of 1890–2050°С, which includes their melting point, has been studied. A method is developed for maintaining crystal in the state of crystal–melt phase transition for a long time, sufficient for carrying out and finishing mechanical tests. Crystal deformation was performed in the creep mode under uniaxial compression along the [10\(\bar {1}\)2] direction. A sharp (stepwise) increase in the creep rate is found when reaching the melting point: it becomes more than an order of magnitude higher as compared with that at near-melting point temperatures. A hypothesis is proposed to explain the found phenomenon by the existence of a transition state between the solid and liquid phases of aluminum oxide, which is characterized by lattice conservation at a sharp increase in the self-diffusion rate.

XANES spectra of protein films (hemoglobin and alkaline phosphatase) formed on the surface of a liquid subphase in a Langmuir trough have been obtained experimentally. The potential of X-ray absorption spectroscopy in the total external reflection geometry is demonstrated by the example of a protein film based on hemoglobin subjected to the action of urea. It is established that the presence of 0.09 M urea solution in the subphase enhances significantly the ability of hemoglobin to bind zinc and iron ions. Information about the local atomic environment of zinc ions bound with a hemoglobin molecule is obtained. It is shown that each zinc ion is coordinated by four ligands, two of which are amino acid residues of cysteine and histidine. The general concepts of the molecular mechanisms of accumulation of metal ions under the action of disturbing factors are formulated.

The phase composition and specific features of the microstructures of layers in the Pb(Zr_0.52Ti_0.48)O₃–LaNiO₃–Si and Pb(Zr_0.52Ti_0.48)O₃–LaNiO₃–SiO_x–Si compositions grown by chemical vapor deposition from solutions have been investigated by high-resolution transmission electron microscopy, electron diffraction, and energy-dispersive analysis. The influence of the structure of the lower LaNiO₃ electrode on the structure and properties of ferroelectric lead zirconate titanate films with a perovskite structure is studied. It is shown that the misoriented porous polycrystalline structure of the lower electrode leads to violation of the columnarity of perovskite grains. The electrical parameters are slightly deteriorated in comparison with a conventional platinum electrode. The structures of the thin films with a silicate sublayer under the LaNiO₃ electrode and without it are compared.

Hydrolysis of TiOSO₄ · xH₂SO₄ · yH₂O and TiOSO₄ · xH₂O, performed in the presence of poly-N-vinylcaprolactam (PVCL) or poly-N-vinylpyrrolidone (PVP) and in an aqueous medium, has provided for the first time samples containing nanophases of, respectively, η-modification of TiO_2 – x · nH₂O ( intercalates TiO_2 – x · (nH₂O, PVCL) or TiO_2 – x · (nH₂O, PVP)) and with anatase structure (TiO₂). The samples have been characterized by X-ray diffraction and X-ray photoelectron spectroscopy. They are found to have different antimicrobial activities. A relationship is established between the antimicrobial activity and the structural features of titanium(IV) oxide; concentration of hydrated titanium dioxide in the samples; and the content of free water and hydroxyl and \({\text{SO}}_{4}^{{2 - }}\) groups on the surface of anatase and η-phase nanoparticles, respectively. The choice of polymer does not affect the antimicrobial activity.

The original process of growing K₂(Co, Ni)(SO₄)₂ · 6H₂O mixed crystals has been mathematically modeled. The specific features of the hydrodynamics and mass transfer for smooth and rough crystallization surfaces are discussed.

The Fe_1 + ySe_xTe_1 – x single crystals grown by the KCl flux and Bridgman methods have been compared using the same investigation techniques. It is shown that the KCl flux growth yields high-quality Fe_1 + ySe_xTe_1 – x superconducting single crystals. The oxygen diffusion coefficient in Fe_1 + ySe_xTe_1 – x has been estimated. During the Bridgman crystal growth, a stable nonsuperconducting phase can be formed, which suggests a need for refining the phase diagram of this compound.

The results of studying an ancient terracotta sculpture found in the Kerch bay are presented. An attempt is made to reconstruct the initial terracotta color and determine the palette composition of ancient painters using a complex of analytical methods: optical and scanning electron microscopy, energy-dispersive X-ray microanalysis, X-ray diffraction, and IR spectroscopy. A study of the terracotta made it possible to reveal a polychromatic character of the decor and determine the composition of the pigments. Iron/manganese compounds were used as a dark brown pigment for coloring the hair, beard, and moustache of the ceramic sculpture. Red ochre and gypsum were applied for coloring lips. Sandarac was used as an adhesive layer for depositing inorganic pigments, as well as a protective layer. The portrait terracotta is suggested to play a role of a ship decoration element.