Sergiy Bokoch - Academia.edu (original) (raw)
Papers by Sergiy Bokoch
Short-range order is a unique natural phenomenon occurring by concentration on heterogeneity, who... more Short-range order is a unique natural phenomenon occurring by concentration on heterogeneity, whose dimensions are commensurate with lattice parameters of the disordered alloy. Kinetics of short-range order is determined by the microscopic diffusion over intersite distances. Therefore, kinetic measurements of its relaxation provide us with
ISRN Thermodynamics, 2012
Within the scope of the self-consistent field and mean (‘‘molecular’’) self-consistent field appr... more Within the scope of the self-consistent field and mean (‘‘molecular’’) self-consistent field approximations, applying the static concentration wave method, the thermodynamics of f.c.c.-Ni–Fe alloys undergoing the static applied magnetic field effects is studied in detail. Under such conditions, the analytical corrections to expressions for the configuration-dependent part of free energy of macroscopically ferromagnetic L12-Ni3Fe-type or L10-NiFe-type ordering phases are taken into account. The obtained results for thermodynamically equilibrium states are compared with the refined phase diagram for f.c.c.-Ni–Fe alloys calculated recently without taking into account the applied magnetic field effects. Considering the specific character of microscopic structure of the magnetic and atomic orders in f.c.c.-Ni–Fe alloys, the changes of shape (and in arrangement) of order-disorder phase-transformation curves (Kurnakov points) are thoroughly analysed. A special attention is addressed to the...
Parameters of a relaxation of resistivity and diffuse scattering in binary substitutional solutions F. C. C.-Ni-Mo
Parameters of microdiffusion in F.C.C.-Ni–Mo solid solutions
Microscopic approach to the evaluation of diffusion coefficients for substitutional F.C.C. solid solutions
A semi-empirical parameterization of interatomic interactions based on the statistical-thermodynamic analysis of the data on radiation diffraction and phase equilibria in F.C.C.-Ni-Fe alloys
Using both the statistical-thermodynamics methods within the scope of the selfconsistent field ap... more Using both the statistical-thermodynamics methods within the scope of the selfconsistent field approximation and the diffraction data on coherent (or diffuse) scattering of X-rays (or thermal neutrons) from (dis)ordered f.c.c.-Ni–Fe alloys of various compositions, the estimation of interatomic interactions (including their magnetic contribution) and their temperature– concentration dependences were obtained. Based on the static concentration-wave representation, the expressions for configuration free energies of L12-Ni3Fe-type permalloy, L10-NiFe-type elinvar and L12-Fe3Ni-type invar were analyzed, considering explicit expressions for configuration entropies of atomic and magnetic subsystems with their configuration internal energies. Phase diagram of a system at issue was plotted within the field of the presence of f.c.c.-Ni–Fe alloys; their phase boundaries, equilibrium (static) properties near critical points (order parameter, etc.), and possible microstructures developed by composition-controlled magnetic transitions and/or order–disorder constant-composition solid–solid phase transformations were discussed. The obtained results were compared with available experimental data.
physica status solidi (a), 2009
The atomic short-range order (SRO) for the substitutional f.c.c.-Ni-9 at.% Al single-crystal solu... more The atomic short-range order (SRO) for the substitutional f.c.c.-Ni-9 at.% Al single-crystal solution is investigated using the X-ray diffuse-scattering method (supplemented by Monte Carlo simulation studies) and analyzing the salient features of the second-order phonon diffuse scattering of X-rays. As shown, in quenched state, the SRO corresponds to the presence in alloy of the static concentration waves with k X (0 0 1) and k(0 0 0.2) wave vectors. Initial SRO-kinetics stage is attended by the noticeable increasing of the diffuse-scattering intensities for wave vectors close to structural (Bragg) reflexes. Parameters of the time dependence of X-ray diffuse-scattering intensity for f.c.c.-Ni-9 at.% Al alloy (after quenching) at low annealing temperature (373 K) are significantly different for different wave vectors generating the ordering and/or clustering processes.
Diffuse scattering intensity near the Bragg reflection in a (para)magnetic bulk face-centred cubic Ni3Fe-type permalloy
Acta Crystallographica Section A Foundations of Crystallography, 2013
Physica C: Superconductivity, 2001
The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO... more The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO parts. The peculiarities of solidification, phase formation, structure transformations and electromagnetic properties of MT-YBCO soldered with Tm Ba 2 Cu 3 O 7-/ are discussed.
Short-range order is a unique natural phenomenon occurring by concentration heterogeneity, whose ... more Short-range order is a unique natural phenomenon occurring by concentration heterogeneity, whose dimensions are commensurate with lattice parameters of the disordered alloy. Kinetics of short-range order is determined by the microscopic diffusion over intersite distances. Therefore, kinetic measurements of its relaxation provide us with more detailed information on the discrete diffusion mechanism such as a possibility to determine the microscopic characteristics of atomic migrations, including probabilities and types of atomic jumps, and activation energy of diffusion. Discrete diffusion measurements can be performed at room temperatures, because of the sufficiently short time scale of elementary diffusion events. It means that results can be utilized to determine the low-temperature diffusivities and activation energies.
Author(s) of this paper may load this reprint on their own web site or institutional repository p... more Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.
ISRN Thermodynamics, 2012
Within the scope of the self-consistent field and mean ('molecular') self-consistent field approx... more Within the scope of the self-consistent field and mean ('molecular') self-consistent field approximations, applying the static concentration wave method, the thermodynamics of f.c.c.-Ni-Fe alloys undergoing the static applied magnetic-field effects is studied in detail. Under such conditions, the analytical corrections to expressions for the configuration-dependent part of free energy of macroscopically ferromagnetic L1 2 -Ni 3 Fe-type or L1 0 -NiFe-type ordering phases are taken into account. The obtained results for thermodynamically-equilibrium states are compared with the refined phase diagram for f.c.c.-Ni-Fe alloys calculated recently without taking into account the applied magnetic field effects. Considering the specific character of microscopic structure of the magnetic and atomic orders in f.c.c.-Ni-Fe alloys, the changes of shape (and in arrangement) of order-disorder phase-transformation curves (Kurnakov's points) are thoroughly analysed. A special attention is addressed to the investigation of the concentration, temperature and magnetic-field induction dependent atomic and magnetic long-range order parameters, especially, near their critical points. As revealed unambiguously, influence of a static applied magnetic field promotes the elevation of Kurnakov's points for all the atomically ordering phases that is in an overall agreement with reliable experimental data. On the base of revealed phenomenon, the magnetoexternal field analog-to-digital converter of the monochromatic radiations (x-rays or thermal neutrons) is hypothesized as a claim.
Long-range crystal-lattice distortion fields of epitaxial Ge-Sb-Te phase-change materials
physica status solidi (b), 2013
ABSTRACT The structural evolution of Ge–Sb–Te-based phase-change material during molecular beam e... more ABSTRACT The structural evolution of Ge–Sb–Te-based phase-change material during molecular beam epitaxy growth is investigated. The in situ and ex situ synchrotron-based X-ray scattering results reveal the formation and evolution of defects-induced inhomogeneities during growth. The scattered intensity in the vicinity of various Bragg reflections indicates a specific scattering vector-dependent anisotropy in the diffuse scattering regime. The average local static distortion fields of the defects-induced inhomogeneities are estimated to be in between 2.5 and 3.0 nm. The defects-induced diffuse scattering anisotropy, observed for the particular Bragg points, arises from the combination of the elastic and crystalline anisotropies that are caused by the large number of vacancies. The experiments show that the large-size defect clusters create inhomogeneity-driven tetragonal fields inserted into the metastable phase of the Ge–Sb–Te host crystal.
С использованием данных, полученных измерением удельного остаточного электрического сопротивления... more С использованием данных, полученных измерением удельного остаточного электрического сопротивления в течение изотермического отжига, изучается кинетика ближнего порядка для твердых растворов замещения ГЦК-Ni-Mo. На основе экспериментальных результатов в рамках модели кинетики первого порядка и (более реалистичной) модели кинетики второго порядка рассчитаны наибольшие характерные времена релаксации удельного остаточного электросопротивления и его равновесные значения для этих растворов при различных температурах отжига и закалки (в пределах интервалов 50-100C и 450-700C соответственно). В рамках гипотезы о совпадении наибольших характерных времен релаксации диффузного рассеяния излучений и остаточного электросопротивления оценены наибольшие характерные времена релаксации для диффузного рассеяния в этих твердых растворах. Построены кривые временно й зависимости нормированного изменения интенсивности диффузного рассеяния излучений, соответствующей той звезде волнового вектора, которая доминирует в отображении структуры ближнего порядка, при разных температурах закалки и отжига для твердых растворов Ni-Mo. З використанням даних, отриманих вимірюванням питомого залишкового електричного опору протягом термічного відпалювання, вивчається кінетика близького порядку для твердих розчинів заміщення ГЦК-Ni-Mo. На основі експериментальних результатів в рамках моделі кінетики першого порядку і (більш реалістичної) моделі кінетики другого порядку розраховано найбільші характерні часи релаксації залишкового питомого електроопору і його рівноважні значення для цих розчинів при різних температурах відпалу і загартування (в межах інтервалів 50-100C і 450-700C відповідно). Оціне-Ìåòàëëîôèç. íîâåéøèå òåõíîë. / Metallofiz. Noveishie Tekhnol. 2002, т. 24, № 5, сс. 691-704 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией 2002 ИМФ (Институт металлофизики им. Г. В. Курдюмова НАН Украины) Напечатано в Украине.
The time evolution of diffuse X-ray scattering intensities conditioned by the short-range order (... more The time evolution of diffuse X-ray scattering intensities conditioned by the short-range order (SRO) in Ni-Mo solid solutions is investigated. As shown, the transition from a quenched (nonequilibrium) state to the equilibrium one is accompanied by the complex time reorganization of various SRO types. Computer simulations of local atomic configurations in alloy with use of the Monte Carlo method, inhomogeneous-SRO model, and calculation of electron density of states (DOS) at the Fermi level give the opportunity of obtaining quantitative characteristics of atomic reconfigurations. The relaxation times of diffuse X-ray scattering intensities and Fourier components of atom jumps for different wave vectors k in reciprocal space are determined. Based on the microdiffusion model for f.c.c. solid solution, the micro- and macroscopic parameters of the atom migration of both components in Ni-Mo solid solutions are investigated.
The microscopic theory of atomic diffusion kinetics is used for f.c.c. substitutional solid solut... more The microscopic theory of atomic diffusion kinetics is used for f.c.c. substitutional solid solutions. Within this approach, the short-range order relaxation is due to the atomic migration. Experimental data on the time dependence of radiation diffuse scattering are used for the determination of microscopic characteristics of atomic migration. The model takes into account the discrete and anisotropic character of atomic jumps in a long-range field of the concentration heterogeneities of interacting atoms. Such a consideration is applied for a close-packed Ni-Fe solid solution. Atomic-jumps' probabilities are estimated that allows to determine the diffusion coefficients and activation energies. Independent kinetic experimental data about a time evolution of long-range order are also used to calculate diffusivities in L1 2 -Ni-Fe alloy.
physica status solidi (a), 2009
Author(s) of this paper may load this reprint on their own web site or institutional repository p... more Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.
Short-range order is a unique natural phenomenon occurring by concentration on heterogeneity, who... more Short-range order is a unique natural phenomenon occurring by concentration on heterogeneity, whose dimensions are commensurate with lattice parameters of the disordered alloy. Kinetics of short-range order is determined by the microscopic diffusion over intersite distances. Therefore, kinetic measurements of its relaxation provide us with
ISRN Thermodynamics, 2012
Within the scope of the self-consistent field and mean (‘‘molecular’’) self-consistent field appr... more Within the scope of the self-consistent field and mean (‘‘molecular’’) self-consistent field approximations, applying the static concentration wave method, the thermodynamics of f.c.c.-Ni–Fe alloys undergoing the static applied magnetic field effects is studied in detail. Under such conditions, the analytical corrections to expressions for the configuration-dependent part of free energy of macroscopically ferromagnetic L12-Ni3Fe-type or L10-NiFe-type ordering phases are taken into account. The obtained results for thermodynamically equilibrium states are compared with the refined phase diagram for f.c.c.-Ni–Fe alloys calculated recently without taking into account the applied magnetic field effects. Considering the specific character of microscopic structure of the magnetic and atomic orders in f.c.c.-Ni–Fe alloys, the changes of shape (and in arrangement) of order-disorder phase-transformation curves (Kurnakov points) are thoroughly analysed. A special attention is addressed to the...
Parameters of a relaxation of resistivity and diffuse scattering in binary substitutional solutions F. C. C.-Ni-Mo
Parameters of microdiffusion in F.C.C.-Ni–Mo solid solutions
Microscopic approach to the evaluation of diffusion coefficients for substitutional F.C.C. solid solutions
A semi-empirical parameterization of interatomic interactions based on the statistical-thermodynamic analysis of the data on radiation diffraction and phase equilibria in F.C.C.-Ni-Fe alloys
Using both the statistical-thermodynamics methods within the scope of the selfconsistent field ap... more Using both the statistical-thermodynamics methods within the scope of the selfconsistent field approximation and the diffraction data on coherent (or diffuse) scattering of X-rays (or thermal neutrons) from (dis)ordered f.c.c.-Ni–Fe alloys of various compositions, the estimation of interatomic interactions (including their magnetic contribution) and their temperature– concentration dependences were obtained. Based on the static concentration-wave representation, the expressions for configuration free energies of L12-Ni3Fe-type permalloy, L10-NiFe-type elinvar and L12-Fe3Ni-type invar were analyzed, considering explicit expressions for configuration entropies of atomic and magnetic subsystems with their configuration internal energies. Phase diagram of a system at issue was plotted within the field of the presence of f.c.c.-Ni–Fe alloys; their phase boundaries, equilibrium (static) properties near critical points (order parameter, etc.), and possible microstructures developed by composition-controlled magnetic transitions and/or order–disorder constant-composition solid–solid phase transformations were discussed. The obtained results were compared with available experimental data.
physica status solidi (a), 2009
The atomic short-range order (SRO) for the substitutional f.c.c.-Ni-9 at.% Al single-crystal solu... more The atomic short-range order (SRO) for the substitutional f.c.c.-Ni-9 at.% Al single-crystal solution is investigated using the X-ray diffuse-scattering method (supplemented by Monte Carlo simulation studies) and analyzing the salient features of the second-order phonon diffuse scattering of X-rays. As shown, in quenched state, the SRO corresponds to the presence in alloy of the static concentration waves with k X (0 0 1) and k(0 0 0.2) wave vectors. Initial SRO-kinetics stage is attended by the noticeable increasing of the diffuse-scattering intensities for wave vectors close to structural (Bragg) reflexes. Parameters of the time dependence of X-ray diffuse-scattering intensity for f.c.c.-Ni-9 at.% Al alloy (after quenching) at low annealing temperature (373 K) are significantly different for different wave vectors generating the ordering and/or clustering processes.
Diffuse scattering intensity near the Bragg reflection in a (para)magnetic bulk face-centred cubic Ni3Fe-type permalloy
Acta Crystallographica Section A Foundations of Crystallography, 2013
Physica C: Superconductivity, 2001
The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO... more The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO parts. The peculiarities of solidification, phase formation, structure transformations and electromagnetic properties of MT-YBCO soldered with Tm Ba 2 Cu 3 O 7-/ are discussed.
Short-range order is a unique natural phenomenon occurring by concentration heterogeneity, whose ... more Short-range order is a unique natural phenomenon occurring by concentration heterogeneity, whose dimensions are commensurate with lattice parameters of the disordered alloy. Kinetics of short-range order is determined by the microscopic diffusion over intersite distances. Therefore, kinetic measurements of its relaxation provide us with more detailed information on the discrete diffusion mechanism such as a possibility to determine the microscopic characteristics of atomic migrations, including probabilities and types of atomic jumps, and activation energy of diffusion. Discrete diffusion measurements can be performed at room temperatures, because of the sufficiently short time scale of elementary diffusion events. It means that results can be utilized to determine the low-temperature diffusivities and activation energies.
Author(s) of this paper may load this reprint on their own web site or institutional repository p... more Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.
ISRN Thermodynamics, 2012
Within the scope of the self-consistent field and mean ('molecular') self-consistent field approx... more Within the scope of the self-consistent field and mean ('molecular') self-consistent field approximations, applying the static concentration wave method, the thermodynamics of f.c.c.-Ni-Fe alloys undergoing the static applied magnetic-field effects is studied in detail. Under such conditions, the analytical corrections to expressions for the configuration-dependent part of free energy of macroscopically ferromagnetic L1 2 -Ni 3 Fe-type or L1 0 -NiFe-type ordering phases are taken into account. The obtained results for thermodynamically-equilibrium states are compared with the refined phase diagram for f.c.c.-Ni-Fe alloys calculated recently without taking into account the applied magnetic field effects. Considering the specific character of microscopic structure of the magnetic and atomic orders in f.c.c.-Ni-Fe alloys, the changes of shape (and in arrangement) of order-disorder phase-transformation curves (Kurnakov's points) are thoroughly analysed. A special attention is addressed to the investigation of the concentration, temperature and magnetic-field induction dependent atomic and magnetic long-range order parameters, especially, near their critical points. As revealed unambiguously, influence of a static applied magnetic field promotes the elevation of Kurnakov's points for all the atomically ordering phases that is in an overall agreement with reliable experimental data. On the base of revealed phenomenon, the magnetoexternal field analog-to-digital converter of the monochromatic radiations (x-rays or thermal neutrons) is hypothesized as a claim.
Long-range crystal-lattice distortion fields of epitaxial Ge-Sb-Te phase-change materials
physica status solidi (b), 2013
ABSTRACT The structural evolution of Ge–Sb–Te-based phase-change material during molecular beam e... more ABSTRACT The structural evolution of Ge–Sb–Te-based phase-change material during molecular beam epitaxy growth is investigated. The in situ and ex situ synchrotron-based X-ray scattering results reveal the formation and evolution of defects-induced inhomogeneities during growth. The scattered intensity in the vicinity of various Bragg reflections indicates a specific scattering vector-dependent anisotropy in the diffuse scattering regime. The average local static distortion fields of the defects-induced inhomogeneities are estimated to be in between 2.5 and 3.0 nm. The defects-induced diffuse scattering anisotropy, observed for the particular Bragg points, arises from the combination of the elastic and crystalline anisotropies that are caused by the large number of vacancies. The experiments show that the large-size defect clusters create inhomogeneity-driven tetragonal fields inserted into the metastable phase of the Ge–Sb–Te host crystal.
С использованием данных, полученных измерением удельного остаточного электрического сопротивления... more С использованием данных, полученных измерением удельного остаточного электрического сопротивления в течение изотермического отжига, изучается кинетика ближнего порядка для твердых растворов замещения ГЦК-Ni-Mo. На основе экспериментальных результатов в рамках модели кинетики первого порядка и (более реалистичной) модели кинетики второго порядка рассчитаны наибольшие характерные времена релаксации удельного остаточного электросопротивления и его равновесные значения для этих растворов при различных температурах отжига и закалки (в пределах интервалов 50-100C и 450-700C соответственно). В рамках гипотезы о совпадении наибольших характерных времен релаксации диффузного рассеяния излучений и остаточного электросопротивления оценены наибольшие характерные времена релаксации для диффузного рассеяния в этих твердых растворах. Построены кривые временно й зависимости нормированного изменения интенсивности диффузного рассеяния излучений, соответствующей той звезде волнового вектора, которая доминирует в отображении структуры ближнего порядка, при разных температурах закалки и отжига для твердых растворов Ni-Mo. З використанням даних, отриманих вимірюванням питомого залишкового електричного опору протягом термічного відпалювання, вивчається кінетика близького порядку для твердих розчинів заміщення ГЦК-Ni-Mo. На основі експериментальних результатів в рамках моделі кінетики першого порядку і (більш реалістичної) моделі кінетики другого порядку розраховано найбільші характерні часи релаксації залишкового питомого електроопору і його рівноважні значення для цих розчинів при різних температурах відпалу і загартування (в межах інтервалів 50-100C і 450-700C відповідно). Оціне-Ìåòàëëîôèç. íîâåéøèå òåõíîë. / Metallofiz. Noveishie Tekhnol. 2002, т. 24, № 5, сс. 691-704 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией 2002 ИМФ (Институт металлофизики им. Г. В. Курдюмова НАН Украины) Напечатано в Украине.
The time evolution of diffuse X-ray scattering intensities conditioned by the short-range order (... more The time evolution of diffuse X-ray scattering intensities conditioned by the short-range order (SRO) in Ni-Mo solid solutions is investigated. As shown, the transition from a quenched (nonequilibrium) state to the equilibrium one is accompanied by the complex time reorganization of various SRO types. Computer simulations of local atomic configurations in alloy with use of the Monte Carlo method, inhomogeneous-SRO model, and calculation of electron density of states (DOS) at the Fermi level give the opportunity of obtaining quantitative characteristics of atomic reconfigurations. The relaxation times of diffuse X-ray scattering intensities and Fourier components of atom jumps for different wave vectors k in reciprocal space are determined. Based on the microdiffusion model for f.c.c. solid solution, the micro- and macroscopic parameters of the atom migration of both components in Ni-Mo solid solutions are investigated.
The microscopic theory of atomic diffusion kinetics is used for f.c.c. substitutional solid solut... more The microscopic theory of atomic diffusion kinetics is used for f.c.c. substitutional solid solutions. Within this approach, the short-range order relaxation is due to the atomic migration. Experimental data on the time dependence of radiation diffuse scattering are used for the determination of microscopic characteristics of atomic migration. The model takes into account the discrete and anisotropic character of atomic jumps in a long-range field of the concentration heterogeneities of interacting atoms. Such a consideration is applied for a close-packed Ni-Fe solid solution. Atomic-jumps' probabilities are estimated that allows to determine the diffusion coefficients and activation energies. Independent kinetic experimental data about a time evolution of long-range order are also used to calculate diffusivities in L1 2 -Ni-Fe alloy.
physica status solidi (a), 2009
Author(s) of this paper may load this reprint on their own web site or institutional repository p... more Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.