Том 59, № 7 (2023)

We have studied the thermal expansion of CaIr4B4, IrB1.1, and CaB6. The results demonstrate that the crystal lattices of these phases expand linearly with temperature and that their thermal expansion coefficients lie in the range (5–10) × 10–6 K–1. We have determined the average microhardness of the CaIr4B4, IrB1.1, and CaB6 phases. The average microhardness of the CaIr4B4 phase is ~15 GPa, which is a factor of 3 lower than that of the CaB6 phase

We have studied the effect of discharge pulse duration in the electrospark deposition process on the structure and properties of FeCrWMoCB metallic glass coatings. The coating thickness has been shown to rise from 19.1 to 39 μm with increasing pulse duration. The heat resistance of the coated samples over 100 h of testing at 700°C was 27 to 176 times that of the steel and it increased with increasing pulse duration. The hardness of the coatings ranged from 11.3 to 11.9 GPa. The coatings have been shown to reduce the friction coefficient and wear of the steel by a factor of up to 3.7 and improve its corrosion resistance.

We have studied Cu–Zn and Cu–Ni containing catalysts on carbon supports based on IR-pyrolyzed chitosan and detonation nanodiamond (DND) and assessed their activity for the methanol steam reforming process. All of the catalysts have demonstrated rather high activity for this process and good stability over 30 h of continuous operation. The DND-based catalysts have been shown to have better performance, which seems to be due to their larger surface area and the nature of the functional groups on their surface. The activity of the bimetallic catalysts and the nature of the supports have been shown to be interrelated.

This paper reports on the preparation of precursors of mixed oxide systems by an electrochemical process based on anodic dissolution of titanium in an electrolyte containing Cl–, NO3–, Al3+, Zr4+, and Y3+ ions in the presence of OH– ions electrogenerated on a cathode, interaction of electrode reaction products, their hydrolysis, and coprecipitation of hydrolyzed species. Synthesis was carried out in a coaxial diaphragmless electrochemical reactor having electrodes differing considerably in area and resulted in the formation of primary particles of precursors to oxide phases through hydrolysis, polycondensation, and crystallization. The proposed approach allows complex titania-based systems to be prepared in the form of anatase and brookite phases stable in the temperature range 80–550°C, and the addition of Al3+ ions leads to the formation of the boehmite phase, which undergoes no changes up to 550°C. Heat treatment of the precipitates at 1100°C raised the degree of crystallinity of the samples, and all of the synthesized oxide systems were found to contain the rutile phase (TiO2) and the mixed oxide TiZrO2. The formation of Ti2Y2O7 makes it possible to stabilize the cubic zirconia phase formed during the electrolysis process, which ensures high mechanical strength, corrosion resistance, and sinterability of ceramic particles based on alumina- and yttria-modified titania and zirconia.

We have studied the effect of the size of copper oxide nanoparticles on their electrical transport properties. The nanoparticles have been synthesized by vacuum arc deposition and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy in order to determine their phase composition and size. The results demonstrate that raising the substrate temperature in the deposition process from 300 to 600 K increases the size of the forming nanoparticles from 5.4 to 37.7 nm. The frequency dependences of the electrical conductivity, dielectric permittivity, and dielectric loss tangent of the CuO nanoparticles in the range form 20 Hz to 1 MHz are influenced by their size. In the size range under consideration, distinctions in the dielectric properties of the nanoparticles can be understood in terms of the competing contributions of the competing contributions of the resistive and capacitive components for the particles and grain/particle boundaries.

The rubidium barium polyphosphate RbBa2(PO3)5 containing impurity bismuth monocations has been prepared via crystallization from a melt with the stoichiometric composition and melts containing excess of rubidium or barium. The samples thus obtained demonstrate broadband photoluminescence in the Near-IR. Analysis of their photoluminescence properties leads us to conclude that they contain two types of emission centers and that predominant formation of one of them depends on melt composition. Our results show that one of the emissive centers is a bismuth monocation substituting for a barium cation and that it forms mainly from barium-deficient melts. The other emissive center, a Bi+ monocation substituting on the rubidium site, results predominantly from crystallization of rubidium-deficient melts.

Using rf cathode sputtering in an oxygen atmosphere, we produced a heterostructure based on the bismuth ferrite (BFO) multiferroic and barium strontium niobate (SBN) ferroelectric: BiFeO3(1000 nm)/Sr0.5Ba0.5Nb2O6(1000 nm)/Pt(001)/MgO(001). It was free of impurity phases and had a root mean square surface roughness within 1% of its thickness. All of the layers in the heterostructure were grown epitaxially. The SBN-50 layer consisted of orientation domains tilted in the plane of the interface by ±18.4° with respect to the MgO substrate axes, and the crystallographic axes of the BFO and Pt layers were parallel to the substrate axes. The ferroelectric polarization of the material at U = 90 V was shown to be 59.3 μC/cm2. Our results demonstrate that, to describe the behavior of the relative dielectric permittivity (ε) of the heterostructure in the range 25–250°C, it is sufficient to take into account the ε(t) data for each layer. The mechanisms underlying the observed effects are discussed.

BiFe2(PO4)3 ceramic powder with controlled chemical and phase compositions has been prepared by evaporation of the salt solution, followed by heat treatment. The powder was consolidated by hot pressing and spark plasma sintering, which allowed high-density (92–98%) BiFe2(PO4)3 ceramics with the α-CaMg2(SO4)3 structure to be obtained. Their thermal diffusivity was investigated by the laser flash method in the range 298–573 K, and the thermal conductivity of the high-density (98%) ceramic was determined. Its thermal conductivity was shown to decrease with increasing temperature. The thermal diffusivity and thermal conductivity (0.9–1.4 W/(m K)) of the BiFe2(PO4)3 ceramics demonstrate that they are heat insulators with high working temperatures.