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Ястребцев, Алексей Алексеевич

Организационные подразделения

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Ястребцев

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Алексей Алексеевич

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Только метаданные
The effect of the synthesis conditions on the structure and phase transitions in Ln2(MoO4)3
(2021) Svetogorov, R. D.; Tsarenko, N. A.; Ponkratov, K. V.; Ognevskaya, N. V.; Popov, V. V.; Menushenkov, A. P.; Yastrebtsev, A. A.; Molokova, A. Y.; Rudakov, S. G.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич; Рудаков, Сергей Геннадьевич
© 2020 Elsevier Masson SASThe effect of the lanthanide cation type and calcination temperature on the structure and phase transitions in Ln2(MoO4)3 molybdates was studied using synchrotron X-ray diffraction, infrared and Raman spectroscopy, photoluminescence, simultaneous thermal analysis and inductively coupled plasma atomic emission spectroscopy. It was found that the crystallization of the precursors at 500∘ C/3 h results in the formation of nanocrystalline powders with the monoclinic structure (sp. gr. I112/b (15)) for Ln2(MoO4)3 (Ln = La–Ho), and a mixture of orthorhombic (sp. gr. Pnca(60)) and tetragonal (sp. gr. I41/a(88)) phases for Yb2(MoO4)3. A further increase in temperature to 1000∘ C leads to a significant rearrangement of the crystal structure, which is largely determined by the lanthanide type. The diagram of phase relations in the Ln2(MoO4)3 molybdates as a function of the Ln3+ cation radius and the calcination temperature has been refined. According to the results of Raman and IR spectroscopy, MoO4 tetrahedra are the main structural units in Ln molybdates. The increased hygroscopicity of heavy lanthanide molybdates (Ln = Ho, Yb) is associated with the presence of empty cavities in the orthorhombic structure. The photoluminescence spectra have shown that EuOn polyhedra in Eu2(MoO4)3 are distorted, and Eu3+ ions occupy several nonequivalent crystallographically different sites with a low symmetry point group.
Только метаданные
Control over crystal, local atomic and electronic structures of cerium chromates/chromites via the synthesis conditions
(2023) Popov, V. V.; Menushenkov, A. P.; Dubyago, F. E.; Yastrebtsev, A. A.; Ivanov, A. A.; Rudakov, S. G.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич; Иванов, Андрей Анатольевич; Рудаков, Сергей Геннадьевич
Только метаданные
The synthesis and studies of crystal/local structures and morphology of hydrated molybdenum oxides
(2021) Khramov, E. V.; Zubavichus, Y. V.; Shchetinin, I. V.; Ponkratov, K. V.; Popov, V. V.; Menushenkov, A. P.; Yastrebtsev, A. A.; Molokova, A. Y.; Pisarev, A. A.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич; Писарев, Александр Александрович
© 2021 Elsevier Inc.The crystal/local structure and morphology of hydrated molybdenum oxides particles obtained by acidic precipitation of molybdates solutions were studied using X-ray diffraction, X-ray absorption spectroscopy, scanning electron microscopy, Raman and IR spectroscopy. The precipitation of ammonium heptamolybdate solutions (pH = 1.00) at room temperature result in the formation of poorly crystallized hydrated molybdenum oxides. At the same time, acidification of the sodium molybdate solutions does not lead to the appearance of precipitates for several days. Heating to 90 °C and aging the reaction suspension prepared from both ammonium heptamolybdate and sodium molybdate results in the formation of prismatic h-MoO3 particles with the hexagonal crystal structure. It was shown that distorted octahedra MoO6 are the basic structural units in the formed hydrated molybdenum oxides. Along with the presence of Mo[dbnd]O and Mo–O bonds, the presence of water molecules, hydroxyl ions, and NH4+ (or Na+) ions was detected in the structure of hydrated MoO3. The type of Mo salt and acid significantly affects the morphology of h-MoO3 particles. Large h-MoO3 particles are formed by aggregation of small ones and Ostwald ripening due to the “dissolution - precipitation” process.
Только метаданные
Influence of the lanthanide on the composition and structure of hydrated Ln chromates
(2021) Svetogorov, R. D.; Ognevskaya, N. V.; Tsarenko, N. А.; Seregina, O. N.; Popov, V. V.; Menushenkov, A. P.; Yastrebtsev, A. A.; Dubyago, F. E.; Rudakov, S. G.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич; Рудаков, Сергей Геннадьевич
© 2021 Institute of Physics Publishing. All rights reserved.The effect of the Ln3+ cation type on the composition and structure of a wide range of hydrated lanthanide chromates (Ln = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Y) has been studied. It was found that hydrated Ln chromates can be divided into several groups in terms of their composition and structure. The synthesized chromates of light lanthanides crystallize into heptahydrates [Ln2(CrO4)3(H2O)5]·2H2O (Ln = La, Pr, Nd, Sm) and tetrahydrate Eu2(CrO4)3·4H2O with a monoclinic structure (sp. gr. Р21/с). The chromates of heavy lanthanides (Ln = Gd, Dy, Ho, Yb, Y) remain X-ray amorphous.
Только метаданные
The Effect of the Ln Type on the Structure and Catalytic Properties of Ln Chromites
(2025) Popov, V. V.; Markova, E. B.; Zubavichus, Y. V.; Menushenkov, A. P.; Yastrebtsev, A. A.; Ivanov, A. A.; Gaynanov, B. R.; Berdnikova, M. M.; Pisarev, A. A.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич; Иванов, Андрей Анатольевич; Гайнанов, Булат Радикович; Бердникова, Мария Михайловна; Писарев, Александр Александрович
Только метаданные
Reversible Valence Transition Eu-3+ ? Eu-2+ ? Eu-3+ in EuxEux Ox (2)+ (3)+ (M = Ti, Zr, Hf) 1-MO3+x /2 : An Analysis of XAFS and XRD Data
(2022) Menushenkov, A. P.; Popov, V. V.; Kuznetsov, A. V.; Molokova, A. Y.; Yastrebtsev, A. A.; Gaynanov, B. R.; Rudakov, S. G.; Менушенков, Алексей Павлович; Попов, Виктор Владимирович; Кузнецов, Алексей Владимирович; Ястребцев, Алексей Алексеевич; Гайнанов, Булат Радикович; Рудаков, Сергей Геннадьевич
The regularities of completely reversible valence transition Eu3+. Eu2+. Eu3+ in complex europium oxides have been investigated using a combination of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XANES + EXAFS) synchrotron methods. The influence of the type of M4+ cations on the reduction and oxidation, as well as the formation and evolution of the crystalline and local structure of the (M = Ti, Zr, Hf) compounds is established. It is shown that oxidation of initially reduced Eu2+MO3 samples leads to the formation of mixed-valence (MV) state Eu2+/Eu3+ with inhomogeneous charge distribution, causing a phase transition with formation of partially amophized intermediate metastable phases Eu3+MO3.5 having a monoclinic structure (sp. gr..1211). An increase in the oxidative annealing temperature to 1000 degrees. facilitates further phase transition with the formation of stable cubic phases Eu M2O7.
Только метаданные
Процессы анионного и катионного упорядочения в соединениях Ln2M2O7 (Ln=La-Dy, Y; M=Zr, Hf)
(2016) Ястребцев, А. А.; Ястребцев, Алексей Алексеевич; Менушенков Алексей Павлович
Только метаданные
Comparative neutron and X-ray diffraction analysis of anionic and cationic ordering in rare-earth zirconates (Ln = La, Nd, Tb, Yb, Y)
(2020) Beskrovnyi, A. I.; Neov, D. S.; Shchetinin, I. V.; Ponkratov, K. V.; Yastrebtsev, A. A.; Popov, V. V.; Menushenkov, A. P.; Ястребцев, Алексей Алексеевич; Попов, Виктор Владимирович; Менушенков, Алексей Павлович
© 2020 Elsevier B.V.The influence of the cation radii ratio (γ = 1.37–1.61) and temperature of the isothermal annealing on the specific features of fluorite – pyrochlore phase transition in Ln2O3: ZrO2 = 1:2 (Ln = La, Nd, Tb, Yb, and Y) systems was investigated by means of Neutron (NPD) and X-ray (XRD) powder diffractions as well as Raman spectroscopy. It was shown that with a decrease in the radius of the Ln cation in the La → Nd → Tb → Y → Yb series, the following sequence of phase transitions is observed: the pyrochlore structure → the structure of defect fluorite → the rhombohedral δ-phase. Significant advantages of NPD over XRD are demonstrated for determining the structural features of the anion sublattice. A detailed description of the parameters of the vibrational modes in Raman spectra for samples with a pyrochlore type of ordering is given, depending on the refined structural parameters.
Только метаданные
Effect of the Chemical and Phase Composition of Nanocrystalline Gadolinium Complex Oxides on the Propane Cracking Process
(2020) Markova, E. B.; Kovtun, S. O.; Tereshina, T. A.; Shchetinin, I. V.; Popov, V. V.; Menushenkov, A. P.; Yastrebtsev, A. A.; Molokova, A. Y.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич
© 2020, Pleiades Publishing, Ltd.Abstract: Effect of the chemical composition and crystal structure type of gadolinium complex oxides on their catalytic activity is studied. It is shown that nanocrystalline powders Gd2Ti2O7, Gd2Zr2O7, and Gd2Hf2O7 form highly symmetrical face-centered сubic crystal structures having localized (in Gd2Ti2O7) and delocalized (in Gd2Zr2O7 and Gd2Hf2O7) oxygen vacancies. At the same time, low-symmetrical crystal structures are formed in Gd2(WO4)3 (the monoclinic structure) and Gd2(МоO4)3 (a mixture of monoclinic and rhombic structures). Catalytic runs show that formation of the cubic structure contributes to an increase in the degree of conversion of propane and causes a shift in cracking temperatures to lower values. Formation of this type of nanocrystalline oxides facilitates the dehydrogenation reaction with propylene selectivity up to 80% at temperatures up to 700 К. Formation of the mixture of monoclinic and rhombic structures in Gd2(МоO4)3 leads to a shift in the degree of conversion to the catalytic temperature range of 700–900 К, in which the dehydrogenation reaction predominates (80%). In the case of the monoclinic structure of Gd2(WO4)3 in the same cracking temperature ranges the process of degradation occurs in parallel; this decreases propylene selectivity to 50% and promotes an increase in the yield of ethylene to 30%.
Только метаданные
Features of the Phase Preferences, Long-and Short-Range Order in Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) with Their Relation to Hydration Behavior
(2022) Zubavichus, Y. V.; Svetogorov, R. D.; Khramov, E. V.; Tsarenko, N. A.; Popov, V. V.; Menushenkov, A. P.; Yastrebtsev, A. A.; Gaynanov, B. R.; Rudakov, S. G.; Ivanov, A. A.; Dubyago, F. E.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Ястребцев, Алексей Алексеевич; Гайнанов, Булат Радикович; Рудаков, Сергей Геннадьевич; Иванов, Андрей Анатольевич
© 2022 by the authors. Licensee MDPI, Basel, Switzerland.The effect of synthesis conditions on the features of the long-and short-range order of Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) powders synthesized via coprecipitation of salts has been studied by a complex of physico-chemical techniques including synchrotron X-ray powder diffraction, X-ray absorption spectroscopy, Raman and infrared spectroscopy, and simultaneous thermal analysis. It was found that crystallization of amorphous precursors begins at 600 °C/3 h and leads to the formation of the monoclinic structure with sp. gr. C12/c1(15) for Ln2(WO4)3 (Ln = Gd, Dy) and with sp. gr. P121/a1(14) for Ln = Yb, whereas crystallization of Ho precursor requires even higher temperature. After annealing at 1000 °C, the P121/a1(14) phase becomes the dominant phase component for all heavy lanthanoid types except for Ln = Gd. It was shown that the Ln (Ln = Dy, Ho, and Yb) tungstates with the P121/a1(14) monoclinic structure correspond to trihydrates Ln2(WO4)3·3H2 O formed due to a rapid spontaneous hydration under ambient conditions. It was concluded that the proneness to hydration is due to a specific structure of the P121/a1(14) phase with large voids available to water molecules. Modifications in the local structure of Ln-O coordination shell accompanying the structure type change and hydration are monitored using EXAFS spectroscopy.