A. A. Rempel

Ural Federal University, Sverolovsk, Sverdlovsk, Russia

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Publications (199)221.58 Total impact

  • S I Sadovnikov · A I Gusev · A V Chukin · A A Rempel
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    ABSTRACT: An in situ study of thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide - monoclinic acanthite α-Ag2S and cubic argentite β-Ag2S - has been carried out for the first time using the high-temperature X-ray diffraction method. The temperature dependencies of the unit cell parameters of acanthite and argentite in the interval of 300-623 K have been determined, and the thermal expansion coefficients of acanthite and argentite have been found. It is shown that the observed difference in the thermal expansion coefficients for nano- and coarse-crystalline acanthite is due to the small particle size of nanocrystalline silver sulfide leading to the growth of anharmonicity of atomic vibrations. It is established by differential thermal analysis that a reversible polymorphic acanthite-argentite phase transformation takes place at ∼449-450 K and the phase transformation enthalpy is equal to ∼3.7-3.9 kJ mol(-1).
    No preview · Article · Jan 2016 · Physical Chemistry Chemical Physics
  • S.I. Sadovnikov · A.V. Chukin · A.A. Rempel’ · A.I. Gusev
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    ABSTRACT: The alpha-Ag2S acanthite-beta-Ag2S argentite phase transformation in nanocrystalline silver sulfide has been studied in situ for the first time using high-temperature X-ray diffraction and scanning electron microscopy. The formation of argentite has been proved by differential thermal analysis. The acanthite-argentite transformation occurs at a temperature of similar to 449-450 K, and its enthalpy is similar to 3.7-3.9 kJ mol(-1). The thermal expansion coefficients of acanthite and argentite have been estimated.
    No preview · Article · Jan 2016 · Physics of the Solid State
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    ABSTRACT: The crystal structure, micro- and nanostructure of coarse- and nanocrystalline powders of ordered vanadium carbide V8C7 have been examined by X-ray and neutron diffraction and electron microscopy methods. The synthesized coarse-crystalline powder of ordered vanadium carbide has flower-like morphology. It was established that the real ordered phase has the composition V8C7-δ (δ ≅ 0.03) deviating from perfect stoichiometric composition V8C7. The vanadium atoms forming the octahedral environment □V6 of vacant sites in V8C7-δ are displaced towards the vacancy □. The presence of carbon onion-like structures was found in the vanadium carbide powders with a small content of free (uncombined) carbon. The nanopowders of V8C7-δ carbide with average particle size of 20–30 nm produced by high-energy milling of coarse-crystalline powder retain the crystal structure of the initial powder, but differ in the lattice deformation distortion anisotropy.
    Full-text · Article · Dec 2015 · Superlattices and Microstructures
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    ABSTRACT: Nonstoichiometric vanadium carbide nanopowders ranging in average particle size from 20 to 40 nm have been prepared by high-energy milling and then vacuum-annealed at temperatures from 600 to 1200°C. The crystal structure, microstructure, morphology, and particle size distribution of the starting, milled, and annealed vanadium carbide powders have been studied by X-ray diffraction, laser diffraction, and scanning electron microscopy. The results demonstrate that vacuum annealing of the VCy nanopowders at temperatures from 600 to 800°C leads to partial carbon loss, compositional changes within the homogeneity range of the disordered cubic phase, and a slight increase in nanoparticle size. Vacuum annealing of the nanopowders at t ≥ 1000°C leads to a considerable carbon loss, the formation of the hexagonal phase V2C along with the cubic carbide VCy , and an appreciable increase in VCy particle size. Thus, vacuum annealing of the nanopowders at 800°C or a lower temperature allows one to vary their composition from VC0.70 to VC0.81, while maintaining the average particle size in the range 50 to 20 nm.
    Full-text · Article · Dec 2015 · Inorganic Materials
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    ABSTRACT: Silver sulfide nanoparticles with non-toxic citrate shell are synthesized by chemical bath deposition from aqueous mixtures of silver nitrate and sodium sulfide in the presence of sodium citrate used as a complexing and stabilizing agent. The prepared nanoparticles have Ag2S core with monoclinic crystal structure functionalized by a carbon-containing citrate shell. By varying the concentrations of reagents it was possible to prepare core-shell nanoparticles with pre-assigned size of Ag2S core from 10 and 50 nm and pre-assigned thickness from 1.5 to 10 nm of citrate shell. A probable mechanism of formation of carbon-containing citrate shell on Ag2S core has been proposed.
    Full-text · Article · Nov 2015 · Chemical Physics Letters
  • Albina A. Valeeva · Svetlana Z. Nazarova · Andrey A. Rempel
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    ABSTRACT: For the first time a magnetic quantum-size effect is found in paramagnetic titanium monoxide nanocrystals with the sizes down to 30nm. In situ measurements in the temperature range from 300 to 1200K showed that the magnetic susceptibility of superstoichiometric titanium monoxide nanocrystals TiOy (y>1) depends not only on the structural state of the sample, but also on the size of nanocrystals. The data analysis both for the ordered and disordered TiOy showed that the reason for inversely proportional dependence of Van-Vleck paramagnetism on the size of titanium monoxide nanocrystals is distortion of local symmetry of titanium and oxygen atoms near the nanocrystal surface. Van-Vleck contribution induced by the atomic-vacancy disordering in titanium monoxide is proportional to the deviation of the long-order parameter from its maximal value.
    No preview · Article · Oct 2015

  • No preview · Article · Oct 2015 · Solid State Phenomena
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    S. I. Sadovnikov · A. I. Gusev · A. A. Rempel
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    ABSTRACT: Powders of silver sulfide Ag2S with an average particle size from ~500 to ~20–40 nm have been synthesized by the chemical bath deposition. The powders with a particle size of ~500 nm have a monoclinic (space group P21/c) acanthite structure (α-Ag2S) and the stoichiometric Ag2S composition. It has been revealed for the first time that silver sulfide nanopowders have the same monoclinic acanthite α-Ag2S structure but a nonstoichiometric composition ~Ag1.93S and contain vacant sites in the metal sublattice. The change in the crystal structure upon the transition from cubic argentite β-Ag2S to monoclinic acanthite α-Ag2S is considered.
    Full-text · Article · Oct 2015 · Doklady Physical Chemistry
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    Aleksandr I. Gusev · Alexey S. Kurlov · Andrey A. Rempel
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    ABSTRACT: The effect of the milling energy of VC0.875 carbide on the microstrain anisotropy of nanocrystalline powders has been characterized by the X-ray diffraction analysis; the observed diffraction reflection broadening is caused mainly by the strain broadening rather than the size one.
    Full-text · Article · Sep 2015 · Mendeleev Communications
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    A. I. Gusev · A. S. Kurlov · A. A. Rempel’
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    ABSTRACT: The anisotropy of strain distortions in nanocrystalline vanadium carbide VC0.875 powders has been experimentally studied using X-ray diffraction. It has been shown that the inclusion of microstrain anisotropy and inhomogeneous broadening in the analysis make it possible to more accurately describe experimental data on diffraction reflection broadening. It has been found that strain distortions mainly contribute to the broadening of diffraction reflections of VC0.875 nanopowders produced by high-energy ball milling.
    Full-text · Article · Sep 2015 · Physics of the Solid State
  • Yu. V. Kuznetsova · A. A. Rempel
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    ABSTRACT: Cadmium sulfide (CdS) nanoparticles have been synthesized in a silicate glass matrix containing ZnO additions. Annealing conditions in the temperature range of the glass transition have been shown to determine the final size of the CdS nanoparticles. The particle size, in turn, influences the optical properties, color, and fundamental absorption edge of the glass. The present results demonstrate that, with increasing CdS nanoparticle size, the absorption edge of the glass experiences a redshift from 330 to 530 nm and its luminescence peak shifts from 450 to 750 nm.
    No preview · Article · Sep 2015 · Inorganic Materials
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    ABSTRACT: A new approach for the synthesis of hybrid nanostructured titania–cadmium sulfide photocatalysts has been suggested. Photocatalysts TiO2 on CdS and CdS on TiO2 were characterized by various techniques including transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The photocatalysts have shown high activity in the partial oxidation of ethanol to acetaldehyde under the action of solar light (λ > 420 nm). The improved activity of the catalysts was attributed to the presence of heterojunctions between CdS and TiO2 nanoparticles that results in a more efficient charge separation as compared with pure CdS or TiO2. A better stability of the catalyst TiO2/CdS was likely due to the formation of a TiO2 protective coating on CdS nanoparticles.
    Full-text · Article · Aug 2015 · Catalysis Communications
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    S. I. Sadovnikov · A. A. Rempel
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    ABSTRACT: Silver sulfide (Ag2S) powders have been synthesized through chemical precipitation from aqueous solutions of silver nitrate, sodium sulfide, and sodium citrate or Trilon B as a complexing agent and stabilizer. The synthesized Ag2S powders have a monoclinic (sp. gr. P21/c) acanthite (α-Ag2S) structure. The colloidal stock solutions decanted from the synthesized precipitate have been shown to be stable for at least a year. The particle size of the silver sulfide in the colloidal solutions and precipitated powders has been evaluated by dynamic light scattering, X-ray diffraction, and BET measurements. The results demonstrate that, varying the relative reactant concentrations in the starting reaction mixture, one can precipitate Ag2S nanoparticles of tailored average size in the range from ≃ 500 to ≃20–30 nm. The size of Ag2S nanoparticles in the stable colloidal solutions obtained is 15–20 nm.
    Full-text · Article · Aug 2015 · Inorganic Materials
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    S.I. Sadovnikov · A.I. Gusev · A.A. Rempel
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    ABSTRACT: Chemical deposition from aqueous solutions of silver nitrate and sodium sulfide was used for synthesis of coarse-crystalline and nanocrystalline silver sulfide Ag2S powders. Sodium citrate was used as a complexing and stabilizing agent during synthesis. X-ray diffraction study shows that synthesized Ag2S powders have monoclinic (space group P21/c) α-Ag2S acanthite type crystal structure. The unit cell of artificial monoclinic silver sulfide Ag2S contains four Ag2S formula units and has the following parameters: a = 0.42264 nm, b = 0.69282 nm, c = 0.95317 nm and β = 125.554°. The size of silver sulfide particles in deposited powders was estimated by the X-ray diffraction and BET methods. By varying the ratio between the concentrations of reagents in the initial reaction mixture it is possible to deposit Ag2S nanoparticles with average size ranging in the interval from ∼1000 to ∼30 nm. Ag2S nanopowders have no deformation distortions of the crystal lattice practically because the microstrains ε in the synthesized powders do not exceed 0.15%. All the Ag2S powders with different particle size have an identical morphology.
    Full-text · Article · Jul 2015 · Superlattices and Microstructures
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    M.G. Kostenko · A.A. Rempel · S.V. Sharf · A.V. Lukoyanov
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    ABSTRACT: A variant of the distribution of structural vacancies at which the crystal structure of ordered compounds simultaneously has a long-range order and correlation short-range order has been proposed and analyzed. The long-range order determines the fraction of vacancies in the atomic and vacancy sublattices of the superstructure formed because of ordering. The correlation short-range order takes into account energy favorable correlations in the arrangement of vacancies, which exist in disordered phases and are not determined by the long-range order. The possibility of the correlation short-range order has been examined by ab initio methods by example of ordering of vacancies in titanium monoxide TiO1.0 according to the type of monoclinic superstructure M5X5mon. It has been shown that partially ordered modifications with the correlation short-range order are energetically favorable as compared to the modifications without the correlation short-range order.
    Full-text · Article · Jul 2015 · JETP Letters
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    ABSTRACT: The activity of hybrid nanostructured core-shell photocatalysts based on cadmium sulfide, titanium dioxide, and silicon dioxide has been investigated in the partial oxidation of ethanol under irradiation with visible light. The SiO2/CdS and TiO2/CdS photocatalysts have been synthesized by the sol-gel method and have been characterized by a variety of physicochemical methods, including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier-transform spectroscopy. The synthesized TiO2/CdS samples exhibit a high activity in the partial photocatalytic oxidation of ethanol to acetaldehyde under irradiation with visible light (λ > 420 nm) in a batch reactor. Their high activity can be due to heterojunctions occurring between cadmium sulfide and titanium dioxide nanoparticles and causing the separation of photogenerated charges.
    Full-text · Article · Jul 2015 · Kinetics and Catalysis
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    S I Sadovnikov · A I Gusev · A A Rempel
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    ABSTRACT: For the first time, the α-Ag2S (acanthite)-β-Ag2S (argentite) phase transformation in nanocrystalline and coarse-crystalline powders of silver sulfide has been observed in situ by the scanning electron microscopy method in real-time. The argentite crystals are formed on the surface of acanthite particles as a result of electron-beam heating. According to the differential thermal analysis data, the transformation occurs at a temperature of ∼449-450 K, and the enthalpy of transformation is equal to ∼3.7-3.9 kJ mol(-1). The presence of α-Ag2S (acanthite)-β-Ag2S (argentite) phase transformation is confirmed in situ by high-temperature X-ray diffraction data.
    Full-text · Article · Jul 2015 · Physical Chemistry Chemical Physics
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    S.I. Sadovnikov · A.I. Gusev · A.A. Rempel
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    ABSTRACT: Electronic Supplementary Information for paper “Artificial silver sulfide Ag2S: Crystal structure and particle size in deposited powders” by S.I. Sadovnikov, А.I. Gusev and А.А. Rempel in Superlattices and Microstructures 83 (2015) 35–47
    Full-text · Dataset · Jul 2015
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    S.I. Sadovnikov · A.I. Gusev · A.A. Rempel
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    ABSTRACT: Electronic Supplementary Information for paper “Artificial silver sulfide Ag2S: Crystal structure and particle size in deposited powders” by S.I. Sadovnikov, А.I. Gusev and А.А. Rempel in Superlattices and Microstructures 83 (2015) 35–47
    Full-text · Dataset · Jul 2015
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    S I Sadovnikov · A I Gusev · A A Rempel
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    ABSTRACT: Electronic Supplementary Information for paper “Nonstoichiometry of nanocrystalline monoclinic silver sulfide” by S.I. Sadovnikov, А.I. Gusev and А.А. Rempel in Phys.Chem.Chem.Phys., 2015, 17, 12466
    Full-text · Dataset · Jul 2015

Publication Stats

1k Citations
221.58 Total Impact Points

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Institutions

  • 2012-2015
    • Ural Federal University
      Sverolovsk, Sverdlovsk, Russia
  • 1985-2015
    • Russian Academy of Sciences
      • • Institute of Chemistry
      • • Institute of Solid State Chemistry, Ural Branch
      Moskva, Moscow, Russia
  • 2011
    • Institute of Solid State Physics RAS
      Chernogolovka, Moskovskaya, Russia
  • 2010
    • Friedrich-Alexander-University of Erlangen-Nürnberg
      Erlangen, Bavaria, Germany
    • Institute of Solid State Chemistry and Mechanochemistry
      Novo-Nikolaevsk, Novosibirsk, Russia
  • 2008
    • Ural State Technical University
      Sverolovsk, Sverdlovsk, Russia
  • 1998-2002
    • Universität Stuttgart
      • • Institute of Theoretical Physics
      • • Institute for Theoretical and Applied Physics
      Stuttgart, Baden-Württemberg, Germany