Institute of Chemistry, Komi Science Center

Synthetic oxide pyrochlores are characterized by a wide range of unique properties. Multi-element pyrochlores doped with several transition elements are of particular interest in terms of the mutual influence of dopants on each other and on the functional properties of the compound. This paper presents the results of a study of the electrical and optical properties of oxide pyrochlore based on bismuth niobate doped with cobalt, chromium, and manganese cations in equimolar amounts. XPS was used to study the charge state of cations in the oxide pyrochlore Bi 1.73 Mn 1/3 Cr 1/3 Co 1/3 Nb 2 O 9 + δ, synthesized by a solid-phase reaction. The XPS spectral parameters for the multi-element pyrochlore were compared with those of transition element oxides. It was shown that pyrochlore exhibits a characteristic shift of the Bi4f and Nb3d spectra toward lower energies by 0.20 and 0.65 eV, respectively. The cobalt and manganese cations are in a mixed charge state, predominantly with an effective charge of +2 and +3. The Cr2p spectrum is a superposition of the spectra of chromium ions in charge states of +3, +4, and +6. It was also established that the ceramic microstructure is low in porosity, formed by fused grains measuring 2 μm. The band gap for the direct allowed transition is 1.85 eV. At 24 °C, the permittivity of the pure and doped samples in the range of 104 – 106 Hz depends weakly on frequency and is 70 and 80, respectively. The dielectric loss tangent for both samples at 1 MHz is 0.002, and the activation energy for high-temperature conductivity is 0.78 and 0.71 eV, respectively. The obtained results can be used to improve the methodology for using the material as, for example, a photocatalyst in the visible spectrum.

The genesis of oolitic carbonates among the lower Meotian sulfate–carbonate–clayey deposits in the Cape Kazantip sections was investigated. Laboratory studies were conducted using several analytical techniques, such as carbonate chemical analysis, optical polarization microscopy with the computer support for photography and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), isotopy, gas chromatography (GC), electron paramagnetic resonance (EPR), infrared (IR) spectroscopy, and X-ray diffractometry (XRD). The obtained results show that the chemical composition of oolitic carbonates is characterized by the constant presence of dolomite (11.93‒40.98%) and clayey (2.42‒19.40%) components, as well as the isotopically heaviest values of carbonate carbon (2.74‒5.40‰). These indicate the formation of oolites in saline water of an extremely shallow coastal lagoon. Gypsum is present in oolite cores and as cement in the oolitic carbonates and conglogravelites. Gypsification of sediments, which occurred at the stage of oolite formation during a sharp sea level fall, could be associated with the participation of sulfate ions from meteoric waters in the removal of sediments into the meteoric-vadose zone, possibly, together with the gas-fluid seepage. The occurrence of bottom gas-fluid seeps is corroborated by the detection of mineralized extracellular polymeric substance (EPS) in oolites, as well as the presence of bacterially induced halite, barite, and high-Mn kutnohorite of the dolomite group. Carbonate minerals in oolites are represented by low- and high-Mg calcites and Ca-dolomite. Distribution of the latter variety indicates the possibly primary sedimentary genesis of dolomite microcrystals in the oolite structure.

Forest fires have a significant effect on the structural and functional organization of ecosystems, affecting all its components. The purpose of the work was to analyze and systematize data on the impact of fires in boreal forests on CO2 emissions from the soil surface and the combustion of forest fuels (CFF). It has been shown that pyrogenesis is one of the leading soil-forming factors affecting the physicochemical properties and reserves of organic matter in the forest litter and upper soil horizons, as well as their temperature regime, especially in light coniferous forests formed by pine and larch. In forest litter, after the forest fire, there has been a decrease in acidity and carbon reserves, and a narrowing of the C : N ratio. The fractional composition of organic matter changes due to the accumulation of combustion products. In the organic horizon, an increase in soil density, base saturation, and the hydrophobicity of soils is noted. This, combined with the death of plant root systems, leads to a decrease in the rate of CO2 emissions from the soil surface. The intensity of fires greatly affects the release of carbon dioxide and the time required to return this indicator to its original state. The effect of fire on the temperature coefficient Q10 can be multidirectional: negative (especially in the case of intensive fire), or positive, or with no effect. It has been found that the inhibition of CO2 emissions and the Q10 value is primarily due to reduction of autotrophic respiration.

Research subject. Lower Paleozoic terrigenous deposits of the northern part of the Lyapin anticlinorium in the Subpolar Urals.Materials and methods. From the quartzite sandstones of the Obeiz Formation, which lies in the lower part of the Paleozoic section of the area under consideration, a monofraction of detrital zircon grains was isolated and their optical and isotope-geochronological U-Pb (LA-SF-ICP-MS) studies were carried out.Results. The analysis of the distribution of age values of zircon grains, taking into account their morphological features, revealed the internal structure and geochemical characteristics, the presence of four age populations of this mineral. Probable sources of the removal of terrigenous material were shown, and the age of formation of the Obeiz Formation was clarified.Conclusions. According to the available paleontological (for the overlying sediments) and newly obtained isotope-geochronological data, the Obeiz Formation is of Early Ordovician (Tremadocian-Floian). Clastic material entered the sedimentation area mainly from local sources of sediment, i.e., nearby massifs of granites and granodiorites. The source of redeposited clastic material was mainly the underlying terrigenous sediments of the Moroi Formation (RF3) and Alkesvozh Formation (Є3-O1).

There has been a great interest in developing the phage-containing remedy against plague caused by antimicrobial resistant strains of Yersinia pestis, which have been increasingly isolated in recent years from sick humans and animals. Studies thus are under way to develop a "phage cocktail", which is expected to be effective against a wide range of pathogenic strains. Our paper sheds light on the role of Y. pestis antigen PsaA in reception of the phage L-413C, which might be a possible component of such a "cocktail". Using optical trapping (OT) and atomic force microscopy (AFM), we showed that PsaA-positive cells and PsaA-coated beads or cantilevers bound more effectively to a substrate coated with L-413C rather than Pokrovskaya phage. Comparing two isogenic strains of Y. pestis (EV and EV∆psaA), we found that when bacteria and phages are co-incubated under slightly acidic pH, as if in a eukaryotic cell, PsaA-positive cells bound the phage L-413C more effectively. There is good evidence to say that L-413C may become a component of a new anti-plague therapy due to its high ability to interact with the pili-forming protein PsaA from the outer membrane of Y. pestis.

Molten-salt titanation of core–shell C/SiC composite fibers was carried out. A KCl, LiCl, and K2TiF6 mixture was used as the reaction medium; the titanating agent was metallic titanium powder. The titanation conditions were 800°C and a stationary argon atmosphere. Ceramics were manufactured from the titanated fibers by hot pressing. The microstructure and phase composition of the fibers and hot-pressed samples were investigated. Ti5Si3 and TiC phases were found to be formed upon titanation, and the Ti5Si3 phase reacted with the carbon core of C/SiC composite fibers during hot pressing to yield titanium carbide TiC as a titanium-containing product. The increasing degree of titanation was found to decrease the porosity and insignificantly increase the strength of the hot-pressed ceramics.