Vol 44, No 5 (2018)

A geometric and topological analysis of the Cs₂₁O₃ metal oxide with the minimal known oxygen content, which is formed from an oxygen-containing melt of metallic Cs, is performed. To identify clusters that are precursors of the crystal structures, special algorithms (ToposPro software package) for decomposing structural graphs into cluster substructures are used. The following precursor clusters involved in the self-assembly of the crystal structures are determined: Cs₁₁O₃ three-octahedral clusters; Cs₆ octahedral clusters; and Cs₄ tetrahedral clusters. The symmetry and topological code of the processes of self-assembly of crystal structures from precursor clusters is reconstructed in the following form: primary chain → microlayer → microframework.

The experimental dependences of the intensity of X-ray fluorescence radiation on the concentration of Fe, Mn, and Ti dissolved in lithium-tetraborate-based glass is obtained. The experimental dependences are compared with the calculated ones. It is shown that the experimental and calculated dependences are described by an equation of the same type previously proposed for describing the intensity of the X-ray fluorescence of silicon.

The results of the study of the charge transfer processes in the thin layers of a Ge_28.5Рb₁₅S_56.5 vitreous system are presented. The power-law dependence of the conductivity on frequency and a decrease in the value of the exponent s with increasing temperature are found. The charge transfer is a thermally activated process and two areas on the temperature dependence of conductivity are present. The activation energies of these areas are Е₁ = 0.20 ± 0.01 and Е₂ = 0.50 ± 0.01 eV, respectively. The obtained results are explained within the scope of the correlated barrier hopping (CBH) model of the hopping conductivity in disordered systems. The main microparameters of the system, namely, the density of the localized state (N), hopping length (R_ω), and the maximal value of the height of the potential barrier (W_M), are calculated.

Using the comparison method of the calculated (the model of point charges) and experimental (Mössbauer spectroscopy and the nuclear magnetic resonance) parameters of the nuclear quadrupole interaction, it is shown that the effective charges of all the atoms of the lattices of the superconducting La_2–xSr_xCuO₄ ceramics correspond to the standard degrees of their oxidation, except for atoms of the planar oxygen, the lowered charge of which is interpreted as the result of localization on them of the hole appearing when La³⁺ ions are substituted by Sr²⁺ ions.

Nanosized La_1–xDy_xPO₄ · nH₂O powders are synthesized by the sol-gel method using direct and reverse precipitation. The formation of a continuous series of hexagonal solid solutions based on LaPO₄ · nH₂O is confirmed by the XRD and DSC/TG methods. A continuous series of monoclinic solid solutions based on LaPO4 is formed at temperatures higher than 600°C. A reflex corresponding to a tetragonal form of DyPO₄ is formed during the calcination of DyPO₄ powder at 850°C. Two types of solid solutions are observed at temperatures of 1000–1200°C, namely, monoclinic solutions based on LaPO₄ (to x ≈ 0.7) and tetragonal solutions based on DyPO₄ (0.90 ≤ x ≤ 1.0). The results are compared depending on the methods of nanopowder synthesis.

Using the liquid-phase methods of synthesis—the coprecipitation of hydroxides and the hydrothermal method—mesoporous xerogels are obtained based on the ZrО₂–Y₂О₃–CeО₂ system with 5–8-nm particles and powders (after the heat treatment of xerogels at 600°C) with a coherent scattering region (CSR) size of 9 to 10 nm and S_sp = 96–156 m²/g. After calcination at 1400°C, the powders are transformed into tetragonal solid solutions with a CSR size of 65 nm in the synthesis by the coprecipitation method, and they are transformed into solid solutions with a CSR size of 84 nm with a high degree of tetragonality of c/a = 1.438–1.431 in the synthesis by the hydrothermal method.

The effect of nanosized fibers of aluminum oxide on the properties of protective coatings based on the silicon–boron carbide–zirconium boride composite is investigated. The coatings applied on different substrates (graphite and ceramics) are compared and the effect of the thermal treatment conditions on the formed coatings is examined. It is demonstrated that the introduced additives do not weaken the coating’s thermal resistance and allow reducing the cost of the coating, darkening the color, and protecting it from erosion.

The evolution of the acid–base properties of the surface of zinc oxide powders during mechanical grinding in an attritor is studied. The study is performed using the methods of the adsorption of acid–base indicators and X-ray photoelectron spectroscopy. Correlations between the results obtained by these methods are established. It is shown that a monotonic decrease in the particle size of ZnO powders is accompanied by a nonmonotonic change in the surface acid–base properties.

The effects occurring on the formation of fractal microstructures in conductive layers of oxide compounds are investigated. It is demonstrated that during a high-density current flow in the layers of indium tin oxides (ITOs) placed on glass substrate a dynamic system is formed with the subsequent formation of a current channel on the layer’s surface, which determines the path of the development of fractal microstructures. Fractal microstructures of varied shapes (spiral, sectoral, and radial) were formed. It is shown that application of an additional polymer thin film on the layers of oxide compounds visualizes the breakdown processes occurring within the structure. Magnified polymer imaging allows to estimate the quality of the layers in contact without high resolution optical equipment. The emergence of luminescence related to the relaxation of excited atoms is identified as the most crucial effect following the formation of fractal structures. This analytical signal is promising in terms of the analysis of the processes of the formation of fractal structures.

The possibility of creating physical barriers with various degrees of permeability in porous glass (PG) plates by local variation in the density of the porous structure of the matrix is demonstrated. The compaction of PG in the volume is provided by exposure to femtosecond laser pulses, while the surface impermeability of the compaction areas is provided by exposure to radiation of the CO₂ laser. This approach to control the density of the PG structure makes it possible to create molecular barriers that represent a physical and/or chemical boundary for molecules located in a porous matrix (with controlled permeability). The discussed technology of the local porosity control opens the way to designing integral photon, fluid, and other types of devices based on PG plates.

Glasses of the 6Na₂O–(24–х)B₂O₃–70SiO₂–хFe₂O₃ system with x ranging from 2 to 10 mol % are studied by dilatometry and X-ray powder diffractometry. The density of the glass is measured and the molar volume is calculated. The heat treatment of the glass is carried out at 550 and 700°C for 96 and 2 h, respectively. Magnetite is formed in the heat-treated glasses and its content increases with the growth of the Fe₂O₃ concentration. In the glasses containing from 4 to 8 mol. % of Fe₂O₃, cristobalite is formed after treatment at 700°C for 2 h. An increase in the density and the glass transition temperature and a decrease in the molar volume is observed with the growth of the iron oxide content.

The reliability of the glass used in spacecraft windows depends on the size of the defects forming upon the impingement of meteoritic particles on a window, as well as the size, density, velocity, and angles of impingement of the particles. In this article, based on the theory of the strength in a double-layer model, formulas are developed that express the dependence of the residual glass strength on the diameter, density, velocity relative to the first cosmic velocity, and angles of impingement of the particles.