viktor sivkov - Academia.edu (original) (raw)

Papers by viktor sivkov

Inorganics

The effect of Zn-doping on the phase composition and optical properties of the Bi2ZnxFe1-xTa2O9.5... more The effect of Zn-doping on the phase composition and optical properties of the Bi2ZnxFe1-xTa2O9.5-Δ (x = 0.3, 0.5, 0.7) was studied. XRD data showed that the samples crystallize in the structural type of pyrochlore (sp. gr.Fd-3m). For all the samples, an admixture of bismuth orthotantalate β-BiTaO4 triclinic modification up to 22.5 wt.% is observed. The content of β-BiTaO4 increases with zinc doping. The unit cell parameter of the pyrochlore phase rises from 10.4878 (x = 0.3) to 10.5154 Å (x = 0.7). The samples are characterized by a porous microstructure with indistinct grain boundaries. Zinc oxide has a sintering effect on ceramics. The charge state of the ions in Bi2ZnxFe1-xTa2O9.5-Δ was investigated by X-ray spectroscopy. NEXAFS and XPS data show that zinc doping does not change the oxidation degree of iron and bismuth ions in pyrochlore. The ions are in the charge states Bi(+3), Fe(+3), Zn(+2). In the Ta4fspectrum, an energy shift of the absorption band towards lower energies b...

Features of Phase Formation of Pyrochlore-type Ceramics Bi2Mg(Zn)1–xNixTa2O9

ACS Omega

Crystals

The possibility of high-temperature solid-phase synthesis of Ni-doped bismuth tantalate pyrochlor... more The possibility of high-temperature solid-phase synthesis of Ni-doped bismuth tantalate pyrochlore, not only from the oxide compounds BiTaO4 and NiO but also using nickel chloride NiCl2 as a precursor, was shown for the first time. The concentration range of the formation of nickel pyrochlore Bi2NixTa2O9−δ (0.85 ≤ x ≤ 1.0) at an equal molar ratio of bismuth(III)/tantalum(V) ions was determined. This indicates that the pyrochlore structure may be stable at 20–33% vacant bismuth sublattice. The influence of non-stoichiometric composition relative to bismuth and tantalum, by the example of Bi2±xNiTa2O9−δ and Bi2NiTa2−xO9−δ (x ≤ 0.5) compositions, on the phase composition of ceramics was studied. X-ray powder diffraction phase analysis of Bi2Ni1+yTa1.75−yO9−δ samples made it possible to determine the solubility limit of nickel ions in the tantalum sublattice. It was shown that the molar ratio of metal atoms (Ta, Ni) in the B2O6 (B-Ni(II), Ta(V)) octahedral sublattice of mixed pyrochlore...

Applied Sciences

The results of the comparative quantitative study of oxygen-containing groups adsorbed on the sur... more The results of the comparative quantitative study of oxygen-containing groups adsorbed on the surface of carbonized sponge scaffold (CSS), highly oriented pyrolytic graphite (HOPG), fullerite C60 and multi-walled carbon nanotubes (MWCNTs) introduced into a high vacuum from the atmosphere without any pre-treatment of the surface are discussed. The studied materials are first tested by XRD and Raman spectroscopy, and then quantitatively characterized by XPS and NEXAFS. The research results showed the presence of carbon oxides and water-dissociation products on the surfaces of materials. It was shown that main source of oxygen content (~2%) on the surface of HOPG, MWCNTs, and C60 powder is water condensed from the atmosphere in the form of an adsorbed water molecule and hydroxyl group. On the CSS surface, oxygen atoms are present in the forms of carbon oxides (4–5%) and adsorbed water molecules and hydroxyl groups (5–6%). The high content of adsorbed water on the CSS surface is due to ...

Materials

A continuous series of solid solutions (Bi1.5Mg0.75−xFexTa1.5O7±Δ (x = 0–0.75)) with the pyrochlo... more A continuous series of solid solutions (Bi1.5Mg0.75−xFexTa1.5O7±Δ (x = 0–0.75)) with the pyrochlore structure were synthesized with the solid-phase method. It was shown that iron, like magnesium, is concentrated in the structure in the octahedral position of tantalum. Doping with iron atoms led to an increase in the upper limit of the thermal stability interval of magnesium-containing pyrochlore from 1050 °C (x = 0) up to a temperature of 1140 °C (x = 1). The unit cell constant a and thermal expansion coefficient (TEC) increase uniformly slightly from 10.5018 Å up to 10.5761 Å and from 3.6 up to 9.3 × 10−6 °C−1 in the temperature range 30–1100 °C. The effect of iron(III) ions on the thermal stability and thermal expansion of solid solutions was revealed. It has been established that the thermal stability of iron-containing solid solutions correlates with the unit cell parameter, and the lower the parameter, the more stable the compound. The TEC value, on the contrary, is inversely p...

Applied Sciences, 2021

The fullerite C60 modified by hot isostatic pressing (HIP) at 0.1 GPa in argon near and beyond it... more The fullerite C60 modified by hot isostatic pressing (HIP) at 0.1 GPa in argon near and beyond its thermal stability region (920–1270 K temperature interval) was studied by X-ray diffractometry, Raman spectroscopy, ultra soft X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy. It was found that the C60 molecules merge into closed nanocapsules with a graphene surface during the thermal treatment. The conducted studies showed that using HIP treatment of the fullerite C60, it is possible to obtain a chemically resistant material with a high hardness and elasticity, as well as a density lower than that of the graphite. This new material, consisting of closed graphene nanocapsules 2–5 nm in size, formed by sp2 covalent bonds between carbon atoms is promising for various applications, and as a basis for the synthesis of new composite materials.

International Journal of Molecular Sciences, 2021

Marine sponges were among the first multicellular organisms on our planet and have survived to th... more Marine sponges were among the first multicellular organisms on our planet and have survived to this day thanks to their unique mechanisms of chemical defense and the specific design of their skeletons, which have been optimized over millions of years of evolution to effectively inhabit the aquatic environment. In this work, we carried out studies to elucidate the nature and nanostructural organization of three-dimensional skeletal microfibers of the giant marine demosponge Ianthella basta, the body of which is a micro-reticular, durable structure that determines the ideal filtration function of this organism. For the first time, using the battery of analytical tools including three-dimensional micro—X-ray Fluorescence (3D-µXRF), X-ray diffraction (XRD), infra-red (FTIR), Raman and Near Edge X-ray Fine Structure (NEXAFS) spectroscopy, we have shown that biomineral calcite is responsible for nano-tuning the skeletal fibers of this sponge species. This is the first report on the presen...

Nanomaterials, 2021

The results of the research of a composite based on multi-walled carbon nanotubes (MWCNTs) decora... more The results of the research of a composite based on multi-walled carbon nanotubes (MWCNTs) decorated with CuO/Cu2O/Cu nanoparticles deposited by the cupric formate pyrolysis are discussed. The study used a complementary set of methods, including scanning and transmission electron microscopy, X-ray diffractometry, Raman, and ultrasoft X-ray spectroscopy. The investigation results show the good adhesion between the copper nanoparticles coating and the MWCNT surface through the oxygen atom bridge formation between the carbon atoms of the MWCNT outer graphene layer and the oxygen atoms of CuO and Cu2O oxides. The formation of the Cu–O–C bond between the coating layer and the outer nanotube surface is clearly confirmed by the results of the O 1s near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) of the Cu/MWCNTs nanocomposite. The XPS measurements were performed using a laboratory spectrometer with sample charge compensation, and the NEXAFS stud...

ACS Omega, 2021

The samples of Ni-doped bismuth magnesium tantalate pyrochlores with the general formula Bi 1.4 (... more The samples of Ni-doped bismuth magnesium tantalate pyrochlores with the general formula Bi 1.4 (Mg 1-x Ni x ) 0.7 Ta 1.4 O 6.3 (x = 0.3, 0.5, 0.7) were obtained by solid-phase synthesis. The crystal structure of the pyrochlore type (sp. gr. Fd3̅ m:2) was clarified by the Rietveld method on the basis of X-ray powder diffraction data. The unit cell parameters increase with the decreasing nickel content in the range from 10.5319(1) to 10.5391(1) Å. The electronic state of atoms is established by the XPS method. According to XPS analysis, bismuth atoms have an effective charge of +3, nickel atoms +(2 + δ), and tantalum ions +(5 -δ). The coefficient of thermal expansion of the lattice of the samples was calculated from high-temperature X-ray structural measurements in the range of -180 to 1050 °C. The average values of linear TECs α in the temperature ranges of 30-570 and 600-1050 °C are 5.1 × 10 -6 and 8.1 × 10 -6 °C-1 , respectively. The monotonicity of the change in the thermal expansion coefficient in the temperature range from -100 to 1050 °C indicates the absence of phase transformations. All samples are dielectric and exhibit high activation energies ∼2.0 eV, moderately high dielectric constants ∼24-28, and tangent dielectric losses ∼0.002 at 1 MHz and 21 °C. The electrical properties of the samples are described by a simple parallel equivalent scheme. The chemical composition of the materials has little effect on the polarizability of the medium or on the value of the activation energy of the conductivity. Ionic processes in investigated materials at frequencies 200-10 6 Hz and at temperatures 100-450 °C were not detected.

Applied Sciences, 2020

Currently, X-ray photoelectron spectroscopy (XPS) is widely used to characterize the nanostructur... more Currently, X-ray photoelectron spectroscopy (XPS) is widely used to characterize the nanostructured material surface. The ability to determine the atom distribution and chemical state with depth without the sample destruction is important for studying the internal structure of the coating layer several nanometers thick, and makes XPS the preferable tool for the non-destructive testing of nanostructured systems. In this work, ultra-soft X-ray spectroscopy methods are used to study hidden layers and interfaces of pyrolytic tungsten carbide nanoscale coatings on the multi-walled carbon nanotube (MWCNT) surfaces. XPS measurements were performed using laboratory spectrometers with sample charge compensation, and Near Edge X-ray Absorption Fine Structure (NEXAFS) studies using the Russian–German dipole beamline (RGBL) synchrotron radiation at BESSY-II. The studied samples were tested by scanning and transmission electron microscopy, X-ray diffractometry, Raman scattering and NEXAFS spectr...

Kondensirovannye sredy i mezhfaznye granitsy = Condensed Matter and Interphases, Mar 20, 2020

Nanocomposites obtained by MOCVD through deposition of pyrolytic chromium layers of different thi... more Nanocomposites obtained by MOCVD through deposition of pyrolytic chromium layers of different thickness on the outer surface of multi-walled carbon nanotubes (MWCNTs) using the "Barkhos" chromium-organic liquid were studied.. These pyrolytic Cr coatings have high microhardness, heat resistance, hydrophobicity, and chemical resistance to hydrochloric and sulphuric acids and alkali melt. The unique physical properties of chromium coatings as well as chemical resistance in a wide temperature range and large external surface of MWCNTs offer great opportunities for the possible applications of the studied nanocomposites. An important problem in this case is the determination of the mechanisms of chromium adhesion to the chemically inert surface of MWCNTs. A promising method of studying the interface between the MWCNT surface and the coating layer is ultra-soft X-ray spectroscopy in the NEXAFS 1s carbon ionization threshold region. However, there are practically no publications on such studies for chromium compounds due to the superposition of the structure of NEXAFS Cr2p absorption spectra on the NEXAFS C1s ionization threshold region. In the present paper, nanocomposites were studied by the total electron yield method using the unique technique of suppressing and measuring the contribution of multiple orders near the C1s absorption edge. The studies of the nanocomposite (pyrolytic Cr)/MWCNT performed by NEXAFS and XPS methods showed: (i) the initial MWCNT features are preserved in the composite spectrum; (ii) there is no signifi cant destruction of the outer layers of MWCNTs; (iii) the interface between the MWCNT and the pyrolytic chromium coating is a multilayer structure. This structure includes the outer surface of the MWCNT, the atoms of which form С-О and C-Cr bonds with the pyrolytic chromium coating, chromium carbide monolayer, and the chromium oxide (Cr 2 O 3) coating layer. The effective thickness of the chromium oxide and chromium carbide coating layers is 1.5 and 0.3 nm respectively, were determined for the studied samples.

Science Advances, 2019

We report a strategy for preserving the structural features of collagen triple helix in turbostra... more We report a strategy for preserving the structural features of collagen triple helix in turbostratic graphite.

REVIEWS ON ADVANCED MATERIALS SCIENCE, 2019

The manganese-doped polymorphs of bismuth orthoniobate were studied using thermal analysis, ESR, ... more The manganese-doped polymorphs of bismuth orthoniobate were studied using thermal analysis, ESR, XPS and NEXAFS spectroscopy. It was shown that the phase transition from the orthorhombic (α) to the triclinic (β) modification can be reversible and it can be achieved by prolonged calcination of samples at 750°C. The DSC curves revealed no thermal effects associated with the phase transformation from the triclinic to the orthorhombic modification near 750°C. In the ESR spectra, the absorption band with g = 3.8 characterized by sextet structure disappeared during the phase transformation from the - to the -form and only the broad component with average intensity was observed at g = 2.2-2.0. According to NEXAFS spectroscopy data, the content of oxidized Mn(III) atoms increased and the content of Mn(II) decreased in the orthorhombic polymorph obtained at 750°C from the tri-clinic modification.

Proceedings of the Komi Science Centre of the Ural Division of the Russian Academy of Sciences, 2019

Статья посвящена исследованию композитных материалов, синтезированных на основе многостенных угле... more Статья посвящена исследованию композитных материалов, синтезированных на основе многостенных углеродных нанотрубок (МУНТ) с покрытиями пиролитических железа (Fe) и хрома (Cr), приготовленых методом химического осаждения смеси металлорганических соединений из паровой фазы. Спектральные зависимости сечения поглощения (СП) в широком интервале энергий 250-900 эВ и в области NEXAFS C1s-, Fe2p-и Cr2p-краев поглощения исследуемых образцов измерялись методом полного электронного выхода с использованием синхротронного излучения (Сu). В работе показано, что поверхностные слои МУНТ композитных материалов не имеют существенного разрушения; тонкие наноразмерные покрытия пиролитических Fe и Cr являются сплошными и представляют собой оксиды Fe 3 O 4 и Cr 2 O 3 . Адгезия Fe 3 O 4 и Cr 2 O 3 обеспечивается благодаря химическим связям между атомами углерода поверхностных слоев МУНТ и атомами кислорода покрытий.

The Spines of Sand Dollar Scaphechinus mirabilis (Agassiz 1863): Analytical and Structural Study

Journal of Advanced Microscopy Research, 2010

ABSTRACT The skeletal structures of Echinodermata have the intriguing biomimetic potential to ser... more ABSTRACT The skeletal structures of Echinodermata have the intriguing biomimetic potential to serve as templates for bio-inspired materials chemistry, architecture and materials science. Up to now, sea urchin skeletons have been the most intensively investigated, due to peculiarities of their biomineralization-related processes and the material properties of their calcified teeth, tests and spines. In contrast to sea urchins, the underlying microstructure and chemistry of the highly perforated spines of sand dollars, especially Scaphechinus mirabilis (Agassiz 1863), have not been subject to much previous investigations. This sand dollar is widely distributed in the northwest of the Pacific Ocean from southern Japan to the Aleutian Islands and is known as the main source of naphtoquinone-based substances, which have recently drawn medical attention for their use as cardiological and ophthalmological drugs. Here we report the first study for the sequential preparation of nanostructurally organized spines of S. mirabilis, using a simple enzymatic and hydrogen peroxide-based treatment. The cleaned spines were investigated by using different bioanalytical (AAS, FTIR, Raman and NEXAFS spectroscopy) and structural (XRD) methods to identify the structural nature and origin of the spine-based biomineral. SEM investigations were employed to better understand the structural peculiarities of the inner organization of the spines on micro- and nanolevels. The possible role of low magnesium calcite detected in S. mirabilis spines is discussed.

Journal of Structural Biology, 2013

Studies on the identification, properties and function of chitin in sponges (Porifera), which are... more Studies on the identification, properties and function of chitin in sponges (Porifera), which are recognized as the first multicellular organisms on Earth, continue to be of fundamental scientific interest. The occurrence of chitin has so far been reported in 21 marine sponge species and only in two inhabiting fresh water. In this study, we present the discovery of α-chitin in the endemic demosponge Ochridaspongia rotunda, found in Lake Ohrid, which dates from the Tertiary. The presence of chitin in this species was confirmed using special staining, a chitinase test, FTIR, Raman and NEXAFS spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). In contrast to the case of marine sponges, chitin in O. rotunda has been found only within its holdfast, suggesting a role of chitin in the attachment of the sponge to the hard substratum. Isolated fibrous matter strongly resemble the shape and size of the sponge holdfast with membrane-like structure.

International Journal of Biological Macromolecules, 2012

Until now, there is a lack of knowledge about the presence of chitin in numerous representatives ... more Until now, there is a lack of knowledge about the presence of chitin in numerous representatives of corals (Cnidaria). However, investigations concerning the chitin-based skeletal organization in different coral taxa are significant from biochemical, structural, developmental, ecological and evolutionary points of view. In this paper, we present a thorough screening for the presence of chitin within the skeletal formations of a poorly investigated Mediterranean black coral, Parantipathes larix (Esper, 1792), as a typical representative of the Schizopathidae family. Using a wide array variety of techniques ( 13 C solid state NMR, Fourier transform infrared (FTIR), Raman, NEXAFS, Morgan-Elson assay and Calcofluor White Staining), we unambiguously show for the first time that chitin is an important component within the skeletal stalks as well as pinnules of this coral.

Nanomaterials, 2020

The paper is devoted to the structure and properties of the composite material based on multi-wal... more The paper is devoted to the structure and properties of the composite material based on multi-walled carbon nanotubes (MWCNTs) covered with pyrolytic iron and chromium. Fe/MWCNTs and Cr/MWCNTs nanocomposites have been prepared by the metal organic chemical vapor deposition (MOCVD) growth technique using iron pentacarbonyl and bis(arene)chromium compounds, respectively. Composites structures and morphologies preliminary study were performed using X-ray diffraction, scanning and transmission electron microscopy and Raman scattering. The atomic and chemical composition of the MWCNTs’ surface, Fe-coating and Cr-coating and interface—(MWCNTs surface)/(metal coating) were studied by total electron yield method in the region of near-edge X-ray absorption fine structure (NEXAFS) C1s, Fe2p and Cr2p absorption edges using synchrotron radiation of the Russian-German dipole beamline (RGBL) at BESSY-II and the X-ray photoelectron spectroscopy (XPS) method using the ESCALAB 250 Xi spectrometer an...