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  • 1. Ambrosch-Draxl, C.
    et al.
    Korzhavyi, Pavel A.
    Uppsala University.
    Johansson, Börje
    Uppsala University.
    First-principles study of oxygen ordering in YBa2Cu3O7-x2000In: Physica. C, Superconductivity, ISSN 0921-4534, Vol. 341, 1997-1998 p.Article in journal (Refereed)
    Abstract [en]

    We have performed first-principles calculations considering different patterns of oxygen/vacancy ordering in the Cu-O chains of YBa2Cu3O7-x. From the total-energy values we determine the effective interactions of the oxygen atoms within the basal plane by using the cluster expansion technique. Furthermore, we discuss the effect of ordering to the density of states at the Fermi level.

  • 2.
    Andersson, David A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles based calculation of binary and multicomponent phase diagrams for titanium carbonitride2008In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 32, no 3, 543-565 p.Article in journal (Refereed)
    Abstract [en]

    In this paper we have used a combined first principles and Calphad approach to calculate phase diagrams in the titanium-carbon-nitrogen system, with particular focus on the vacancy-induced ordering of the substoichiometric carbonitride phase, TiCxNy (x + y <= 1). Results from earlier Monte Carlo simulations of the low-temperature binary phase diagrams are used in order to formulate sublattice models for TiCxNy within the compound energy formalism (CEF) that are capable of describing both the low temperature ordered and the high-temperature disordered state. We parameterize these models using first-principles calculations and then we demonstrate how they can be merged with thermodynamic descriptions of the remaining Ti-C-N phases that are derived within the Calphad method by fitting model parameters to experimental data. We also discuss structural and electronic properties of the ordered end-member compounds, as well as short range order effects in the TiCxNy phase.

  • 3.
    Andersson, David A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Thermodynamics of structural vacancies in titanium monoxide from first principles calculations2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 14, 144101- p.Article in journal (Refereed)
    Abstract [en]

    The structure, stability and electronic properties of the low oxygen oxides of titanium, TiOx with 1/3 <= x <= 3/2, have been studied by means of accurate first-principles calculations. In both stoichiometric and nonstoichiometric TiO there are large fractions of vacant lattice sites. These so-called structural vacancies are essential for understanding the properties and phase stability of titanium oxides. Structures with an ordered arrangement of vacancies were treated with a plane wave pseudo-potential method, while calculations for structures with disordered vacancies were performed within the framework of the Korringa-Kohn-Rostoker Green's function technique. The relaxed structural parameters in general compare well with experimental data, though some discrepancies exist for stoichiometric TiO in the ideal B1 structure, i.e., without any vacancies. The equation of state as well as the elastic properties are also derived. A monoclinic, vacancy-containing, structure of stoichiometric TiO is confirmed to be stable at low temperature and pressure. Experimentally a transition from a stoichiometric cubic structure with disordered vacancies to the ideal B1 structure without any vacancies has been observed at high pressure. It is discussed how this experimental observation relates to the present theoretical results for defect-containing and defect-free TiO.

  • 4.
    Baykov, Vitaly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Isaev, P. A.
    Moscow State Institute of Steel and Alloys.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vekilov, Y. K.
    Moscow State Institute of Steel and Alloys.
    Abrikosov, I. A.
    Linköping University.
    Ab Initio Studies of the Energy Characteristics and Magnetic Properties of Point Defects in GaAs2005In: Physics of the solid state, ISSN 1063-7834, E-ISSN 1090-6460, Vol. 47, no 10, 1831-1836 p.Article in journal (Refereed)
    Abstract [en]

    The formation energies of intrinsic point defects and solution energies of transition metal impurities in gallium arsenide are determined on the basis of ab initio calculations using the method of a locally self-consistent Green's function, which is a generalization of the coherent potential approximation. Based on the calculated energies, the conclusion is made that the As-Ga antisite defect is the most common intrinsic defect in GaAs. Calculations showed that transition metal impurities, except for Ni, preferentially occupy gallium sites substitutionally. The magnetic moments of impurity atoms are calculated as a function of the chemical environment. It is shown that, in compensated GaAs, Mn atoms tend to form clusters.

  • 5.
    Baykov, Vitaly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jerlerud Perez, Rosa
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Structural stability of intermetallic phases in the Zr-Sn system2006In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 55, no 5, 485-488 p.Article in journal (Refereed)
    Abstract [en]

    A thermodynamic description of the intermetallic compounds in the Zr-Sn binary system has been obtained using total energy calculations by means of the Vienna ab initio simulation package. Our calculations show that hexagonal compounds Zr5Sn4 and Zr5Sn3 are the most stable phases in the Zr-Sn binary system. Their high stability is found to be due to hybridization of the Sn 5p with Zr 4d electronic states. Based on the calculated energies, the conclusion is made that Zr substitution on the Sri sites takes place in the Zr4Sn phase, which accounts for the unusual stoichiometry of this Cr3Si structure type compound.

  • 6.
    Baykov, Vitaly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Diffusion of Interstitial Mn in the Dilute Magnetic Semiconductor (Ga,Mn)As: The Effect of a Charge State2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 101, no 17, 177204- p.Article in journal (Refereed)
    Abstract [en]

    Migration barriers for diffusion of interstitial Mn in the dilute magnetic semiconductor (Ga,Mn)As are studied using first-principles calculations. The diffusion pathway goes through two types of interstitial sites: As coordinated and Ga coordinated. The energy profile along the path is found to depend on the ratio of concentrations between substitutional and interstitial Mn in GaAs. Two regions of distinctly different behavior, corresponding to n-type and p-type (Ga,Mn)As, are identified. The difference in mobility is a reflection of the change in the charge state of Mn interstitials (double donors) that occurs in the presence of substitutional Mn impurities (acceptors). In addition, substitutional Mn impurities are shown to act as traps for interstitial Mn. The effective migration barrier for the positively doubly charged Mn interstitials in p-type (Ga,Mn)As is estimated to vary from 0.55 to about 0.95 eV.

  • 7.
    Baykov, Vitaly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Smirnova, E. A.
    Department of Theoretical Physics of Steel and Alloys, Moscow.
    Abrikosov, I. A.
    Department of Physics and Measurement Technology, Linköping University.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Magnetic properties of 3d impurities in GaAs2007In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 310, no 2, 2120-2122 p.Article in journal (Refereed)
    Abstract [en]

    Electronic structure, thermodynamic, and magnetic properties of 3d-transition metal (TM) impurities in GaAs have been studied from first principles using Green's function approach. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The possibility of raising the Curie temperature TC in (GaMn) As by co-doping it with Cr impurities was examined on the basis of total energy difference between the disordered local moment (DLM) and the ferromagnetically ordered (FM) spin configurations. The calculated Curie temperature and magnetic moment have maxima for GaAs doped with Cr and Mn. The magnetic properties of Mn-doped GaAs are shown to be more sensitive to antisite As defects than those of Cr-doped GaAs. However, the Cr impurities are sensitive to the presence of acceptor defects, such as vacancies on the Ga sublattice. The investigation of the electronic structure of pseudo-ternary alloys (Ga(1-x-y)MnxCry) As has shown a mutual compensation of Mn and Cr impurities. Therefore, in order to reach the highest critical temperature, GaAs has to be separately doped with Cr or Mn impurities. The GaAs doped with Fe is found to be non-ferromagnetic.

  • 8.
    Bergqvist, Lars
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eriksson, O
    Kudrnovsky, J
    Drchal, V
    Korzhavyi, Pavel
    KTH, Superseded Departments, Materials Science and Engineering.
    Turek, I
    Magnetic percolation in diluted magnetic semiconductors2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 13, 137202- p.Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the magnetic properties of diluted magnetic semiconductors are dominated by short ranged interatomic exchange interactions that have a strong directional dependence. By combining first principles calculations of interatomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations, we reproduce the observed critical temperatures of a broad range of diluted magnetic semiconductors. We also show that agreement between theory and experiment is obtained only when the magnetic atoms are randomly positioned. This suggests that the ordering of diluted magnetic semiconductors is heavily influenced by magnetic percolation, and that the measured critical temperatures should be very sensitive to details in the sample preparation, in agreement with observations.

  • 9.
    Bergqvist, Lars
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sanyal, B.
    Mirbt, S.
    Abrikosov, I. A.
    Nordstrom, L.
    Smirnova, E. A.
    Mohn, P.
    Svedlindh, P.
    Eriksson, O.
    Magnetic and electronic structure of (Ga1-xMnx)As2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 20, 205201- p.Article in journal (Refereed)
    Abstract [en]

    We present theoretical calculations of the magnetic and electronic structure of Mn-doped GaAs (in the zinc-blende structure). The magnetic properties are shown to be very sensitive to structural defects, in particular, As antisite defects and Mn at interstitial positions. Only when considering such defects can the experimental magnetic moments be reproduced by first-principles theory. We present a simple model for understanding the connection between the magnetic ordering and the As antisites, and the way in which the defects help to stabilize a partial disordered local-moment state. The connection between the energetics of the Mn substitution and the As antisite concentration is also analyzed. In addition, we compare the calculated magnetic properties and electronic structures of Mn situated on substitutional sites (Mn replacing a Ga atom) and on interstitial sites, where in agreement with observations the interstitial site is found to be less favorable. Finally, combining our first-principles calculations of the spin-wave excitation energies with a classical Heisenberg Hamiltonian we have calculated interatomic exchange interactions, and using Monte Carlo simulations we present theoretical values of the critical temperature as a function of Mn concentration.

  • 10.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ehtehsami, Hossein
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Chen, Qing
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    New description of metastable hcp phase for unaries Fe and Mn: Coupling between first-principles calculations and CALPHAD modeling2016In: Physica Status Solidi B, ISSN 1521-3951, no 9, 1830-1836 p.Article in journal (Refereed)
    Abstract [en]

    The main focus in developing the third generation of CALPHADdatabases is to model thermodynamic properties of materialsby using models which are more physically based andvalid down to 0K. First-principles calculations are helpful tochoose and validate those models. Reliable calculation results,for example, at very low temperatures or on metastable systemsreveal physical facts which might be inaccessible by experiments.Following our earlierwork for modeling thermodynamicproperties of pure elements (i.e., Fe and Mn) in third-generationCALPHAD databases, the (hcp) phase was modeled as ametastable phase in the present work. Although hcp phase isjust observed in these two elements under ultra-high pressure, inthe binary Fe–Mn this phase is metastable at ambient temperaturesand pressures. Therefore, it should be properly modeled inunaries for later optimization of binary systems. Based on densityfunctional theory (DFT) calculations, the magnetic groundstate and the magnetic properties of -Fe, -Mn, and their binarysolution phase were calculated. It was found that -Fe is antiferromagnetic(type II) while -Mn has a paramagnetic groundstate. Accordingly, magnetic contributions to thermodynamicproperties were accurately modeled. Moreover, by means ofthe extrapolation of experimental data for the thermodynamicproperties of binary systems and high-pressure data for unaries,the metastable hcp phases at ambient pressure were modeledfor the third-generation CALPHAD database, consistently withother stable phases in the elements Fe and Mn.

  • 11. Bleskov, I. D.
    et al.
    Smirnova, E. A.
    Vekilov, Y. K.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Katsnelson, M.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Abrikosov, I. A.
    Isaev, E. I.
    Ab initio calculations of elastic properties of Ru1-xNixAl superalloys2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 16Article in journal (Refereed)
    Abstract [en]

    Ab initio total energy calculations based on the exact muffin-tin orbitals method, combined with the coherent potential approximation, have been used to study the thermodynamical and elastic properties of substitutional refractory Ru1-xNixAl alloys. We have found that the elastic constants C' and C11 exhibit pronounced peculiarities near the concentration of about 40 at. % Ni, which we ascribe to electronic topological transitions. Our suggestion is supported by the Fermi surface calculations in the whole concentration range. Results of our calculations show that one can design Ru-Ni-Al alloys substituting Ru by Ni (up to 40 at. %) with almost invariable elastic constants and reduced density.

  • 12.
    Delandar, Arash Hosseinzadeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gorbatov, O. I.
    Gornostyrev, Yu. N.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ab-initio based search for late blooming phase compositions in iron alloysManuscript (preprint) (Other academic)
  • 13.
    Delandar, Arash Hosseinzadeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    The role of glide during creep of copper at low temperaturesManuscript (preprint) (Other academic)
  • 14.
    Ehteshami, Hossein
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Sun, W.
    Korzhavyi, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Russian Academy of Sciences, Ekaterinburg, Russian Federation.
    Statics and dynamics of point defects in TiC2015In: Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials, International Conference on Solid-Solid Phase Transformations in Inorganic Materials , 2015, 951-958 p.Conference paper (Refereed)
    Abstract [en]

    Here we present the results of a systematic ab initio study of point defects in titanium carbide. The electronic and atomic structure for the metal and non-metal vacancies, interstitials, and antisite defects (including the split interstitial and split antisite conformations) is calculated within the generalized gradient approximation of density functional theory, using the projector augmented wave method as implemented in the Vienna Abinitio Simulation Package VASP. In many cases the symmetric point defect configuration is found to be unstable against a symmetry-breaking distortion via the Jahn-Teller mechanism. An enhanced stability of titanium dumbbells is obtained for sub-stoichiometric TiC1-x where the dumbbells form clusters with the carbon vacancies. Possible migration pathways for point defects and their clusters are explored in order to create a database of possible mechanisms of self-diffusion in TiC.

  • 15. Eloirdi, R.
    et al.
    Gouder, T.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Wastin, F.
    Rebizant, J.
    Dilution effect on the U-5f states: U in an Ag matrix2005In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 386, no 1-2, 70-74 p.Article in journal (Refereed)
    Abstract [en]

    The electronic structure of U-diluted in an Ag matrix has been studied in situ by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). UxAg100-x thin films (x = 0-100 at.%) were produced by sputter co-deposition in an Ar atmosphere. UPS spectra of the Ag-4d line indicate formation of a homogeneous mixture despite the fact that U and Ag do not form stable alloys. A major goal of this work was to find out whether the dilution of U atoms in an inert matrix with no bonding states induces the localisation of the U-5f states. Both U-4f core level spectra and the U-5f spectra indicate U-5f delocalisation, down to 5 at.% of uranium in UxAg100-x films.

  • 16. Eriksson, O
    et al.
    Bergqvist, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Sanyal, B
    Kudrnovsky, J
    Drchal, V
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Turek, I
    Electronic structure and magnetism of diluted magnetic semiconductors2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 48, S5481-S5489 p.Article in journal (Refereed)
    Abstract [en]

    The electronic structure and magnetism of selected diluted magnetic semiconductors (DMS) is reviewed. It is argued that the effect of antisite defects plays an important role in the magnetism of DMS materials and that these defects lower the saturation moment and ordering temperature. We also show that the interatomic exchange of these materials is short ranged. By combining first principles calculations of interatomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations, we show that-the observed critical temperatures of a broad range of diluted magnetic semiconductors, involving Mn-doped GaAs and GaN as well as Cr-doped ZnTe, are reproduced with good accuracy. We show that agreement between theory and experiment is obtained only when the magnetic atoms are randomly positioned on the Ga (or Zn) sites. This suggests that the ordering of DMS materials is heavily influenced by magnetic percolation and that the measured critical temperatures should be very sensitive to details in the sample preparation, in agreement with observations.

  • 17. Fu, Yu-dong
    et al.
    Wang, Baochang
    Teng, Yue
    Zhu, Xiao-shuo
    Feng, Xiao-xue
    Yan, Mu-fu
    Korzhavyi, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Russian Acad Sci, Russia.
    Sun, Weiwei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Vanderbilt Univ, USA.
    The role of group III, IV elements in Nb(4)AC(3) MAX phases (A = Al, Si, Ga, Ge) and the unusual anisotropic behavior of the electronic and optical properties2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 23, 15471-15483 p.Article in journal (Refereed)
    Abstract [en]

    Niobium based Nb4AlC3, Nb4SiC3, Nb4GeC3 and Nb4GaC3 were investigated by means of density functional theory. Together with the known Nb4AlC3, the role of group III, IV elements in various properties of Nb(4)AC(3) (A = Al, Si, Ga, Ge) was systematically investigated, and particularly the bulk moduli, shear moduli, and Young's moduli helped us to approach the ductility. All the studied compounds were found to be mechanically stable, and they also exhibit the metallic nature that results from the Nb-4d states being dominant at the Fermi level. The typical 4d-2p hybridization leads to strong Nb-C covalent bonding and a relatively weaker 4d-3p (4p) hybridization between Nb and A is identified. The latter does perturb the performance of materials. By varying A elements in Nb(4)AC(3), the position and the width of the p states as well as hybridizations are altered, which determine the covalency and the ionicity of the chemical bonds. A high density of states at the Fermi level and the nesting effects in the Fermi surface are identified in Nb4SiC3 and linked to its unusual anisotropic behavior. Furthermore, Nb4GeC3 is predicted to be a very promising candidate solar heating barrier material. Overall, the present work gives insights into the role of A elements in the electronic structure and the physical properties of Nb(4)AC(3) compounds. The tendencies and rules established here will help in the designing of functional ceramic materials with desirable properties.

  • 18.
    Gorbatov, O. I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute of Quantum Materials Science, Russian Federation; Nosov Magnitogorsk State Technical University, Russian Federation.
    Gornostyrev, Yu. N.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute of Metal Physics, Russian Federation.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben Forschung GmbH, Austria.
    Ab initio modeling of decomposition in iron based alloys2016In: Physics of metals and metallography, ISSN 0031-918X, E-ISSN 1555-6190, Vol. 117, no 13, 1293-1327 p.Article in journal (Refereed)
    Abstract [en]

    This paper reviews recent progress in the field of ab initio based simulations of structure and properties of Fe-based alloys. We focus on thermodynamics of these alloys, their decomposition kinetics, and microstructure formation taking into account disorder of magnetic moments with temperature. We review modern theoretical tools which allow a consistent description of the electronic structure and energetics of random alloys with local magnetic moments that become totally or partially disordered when temperature increases. This approach gives a basis for an accurate finite-temperature description of alloys by calculating all the relevant contributions to the Gibbs energy from first-principles, including a configurational part as well as terms due to electronic, vibrational, and magnetic excitations. Applications of these theoretical approaches to the calculations of thermodynamics parameters at elevated temperatures (solution energies and effective interatomic interactions) are discussed including atomistic modeling of decomposition/clustering in Fe-based alloys. It provides a solid basis for understanding experimental data and for developing new steels for modern applications. The precipitation in Fe-Cu based alloys, the decomposition in Fe-Cr, and the short-range order formation in iron alloys with s-p elements are considered as examples.

  • 19. Gorbatov, O. I.
    et al.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Gornostyrev, Yu. N.
    Dependence of vacancy-solute interactions on magnetic state in dilute iron-based alloys2011In: Solid-Solid Phase Transformations in Inorganic Materials: Part 2 / [ed] Y. Brechet, E. Clouet, A. Deschamps, A. Finel, F. Soisson, Zurich-Durnten, Switzerland: TRANS TECH PUBLICATIONS , 2011, 979-984 p.Conference paper (Refereed)
    Abstract [en]

    Vacancy-solute interactions play a crucial role in diffusion-controlled phase transformations, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. The knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) under irradiation, as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on density functional theory and employing the locally self-consistent Green’s function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Ti – Cu), and 4d (Nb – Ag) elements. Interactions within the first two coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a very strong effect on the vacancy-solute interactions.

  • 20. Gorbatov, O. I.
    et al.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Gornostyrev, Yu. N.
    Vacancy-solute interactions in ferromagnetic and paramagnetic bcc iron: Ab initio calculations2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 419, no 1-3, 248-255 p.Article in journal (Refereed)
    Abstract [en]

    Vacancy-solute interactions play a crucial role in diffusion-controlled processes, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. Detailed knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on the density functional theory and employing the locally self-consistent Green's function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Sc-Cu), and 4d (Y-Ag) elements. Unrelaxed interactions within the first three coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a strong effect on the vacancy-solute interactions. Implications of the obtained results for interpreting the effects of vacancy trapping and enhanced impurity diffusion are discussed.

  • 21. Gorbatov, O. I.
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Gornostyrev, Yu.N.
    Effect of magnetism on precipitation of Cu in bcc Fe: Ab-initio based modeling2009In: Scientific basis for nuclear waste management XXXIII, Materials Research Society, 2009, 469-476 p.Conference paper (Refereed)
    Abstract [en]

    Theoretical modeling of the decomposition in bcc Fe-Cu alloys has been performed using a combined approach which includes ab-initio calculations of the effective cluster interactions and statistical-mechanical (Monte Carlo) simulations. We showed that the effective Cu-Cu and Cu-vacancy interactions in the bcc Fe matrix have a strong dependence on the global magnetic state of iron. As a result, all the related thermodynamic properties of the alloys (such as solubility limit and diffusivity) are expected to have a pronounced non-Arrhenius temperature behavior, originated from variation of the global magnetization with temperature. We find that strong Cu-vacancy interactions in the bcc Fe matrix lead to a remarkable effect of vacancies on the Cu precipitation and significantly modify the alloy decomposition kinetics under irradiation.

  • 22.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute of Quantum Materials Science, Russian Federation; Nosov Magnitogorsk State Technical University, Russian Federation.
    Delandar, Arash Hosseinzadeh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gornostyrev, Y. N.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. ENHETEN EGENSKAPER.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    First-principles study of interactions between substitutional solutes in bcc iron2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 475, 140-148 p.Article in journal (Refereed)
    Abstract [en]

    Using density functional theory based calculations, employing the locally self-consistent Green's function method and the projected augmented wave method, we develop a database of solute-solute interactions in dilute alloys of bcc Fe. Interactions within the first three coordination shells are computed for the ferromagnetic state as well as for the paramagnetic (disordered local moment) state of the iron matrix. The contribution of lattice relaxations to the defect interaction energy is investigated in the ferromagnetic state. Implications of the obtained results for modeling the phenomena of point defect clustering and phase precipitation in bcc Fe-based alloys and steel are discussed.

  • 23.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Nosov Magnitogorsk State Technical University, Russian Federation.
    Gornostyrev, Y. N.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute of Metal Physics, Russian Federation.
    Many-body mechanism of Guinier-Preston zones stabilization in Al–Cu alloys2017In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 138, 130-133 p.Article in journal (Refereed)
    Abstract [en]

    Thermodynamics and atomic structures of pre-precipitates in dilute Al–Cu alloys are studied using Metropolis Monte Carlo simulations with many-body effective cluster interactions that have been systematically derived from ab initio supercell calculations. We show that many-body interactions, including the contributions due to lattice relaxations around the solute atoms, are mainly responsible for the formation of metastable planar atomic arrangements known as Guinier-Preston zones. Interaction terms up to four-body clusters are shown to be necessary to correctly reproduce the structures and temperatures of pre-precipitation in Al–Cu solid solutions.

  • 24.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute of Quantum Materials Science, Russian Federation.
    Gornostyrev, Yu. N.
    Institute of Quantum Materials Science, Russian Federation.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute of Metal Physics, Russian Federation .
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben, Austria .
    Effect of Ni and Mn on the formation of Cu precipitates in α-Fe2015In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 102, 11-14 p.Article in journal (Refereed)
    Abstract [en]

    Decomposition in bcc Fe-Cu-Ni and Fe-Cu-Mn alloys is studied using statistical thermodynamics simulations with ab initio effective interactions. It is demonstrated that magnetic state strongly affects the effective interactions in these systems, substantially increasing phase separation tendency with magnetization. Simulations show that Ni is promoting precipitation of Cu by segregating to the precipitate matrix interface, while Mn produces almost no effect distributing more homogeneously in the system. The obtained distributions of Ni and Mn are in good agreement with experimental data.

  • 25.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Okatov, S. V.
    Gornostyrev, Yu N.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Effect of magnetism on the solubility of 3d elements in BCC iron: Results of first-principle investigations2013In: Physics of metals and metallography, ISSN 0031-918X, Vol. 114, no 8, 642-653 p.Article in journal (Refereed)
    Abstract [en]

    The methods of quantum-mechanical simulation have been used to study alloys of bcc iron with 3d transition metals in the ferromagnetic and paramagnetic states. It has been shown that the main factor that determines the solubility of the 3d elements is their electronic structure. The energy of the solution, mixing, and effective interatomic interactions vary regularly depending on the position of the element in the Periodic Table and on the magnetic state of the matrix. In some cases, depending on the magnetic state, changes in these quantities lead to the violation of the Hume-Rothery rules that determine the solubility of substitutional elements in alloys. The results obtained help us to understand the microscopic mechanisms that determine the solubility of alloying elements and their effect on the phase stability and structural state of steels.

  • 26.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Razumov, I. K.
    Gornostyrev, Yu N.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Role of magnetism in Cu precipitation in alpha-Fe2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 17, 174113- p.Article in journal (Refereed)
    Abstract [en]

    The temperature-dependent solubility of Cu in alpha-Fe and initial stages of Cu precipitation are investigated in first-principles calculations and statistical thermodynamic and kinetic modeling based on ab initio effective interactions. We demonstrate that the weakening of the phase separation tendency with increasing temperature, especially close to the magnetic phase transition, is related to the strong dependence of the "chemical" interactions on the global magnetic state. At the same time, our calculations demonstrate that the vibrational contribution obtained in the quasiharmonic approximation is relatively small for temperatures near the Curie point. The results of Monte Carlo simulations of Cu solubility and clustering are in good agreement with experimental data.

  • 27. Granas, O.
    et al.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kissavos, A. E.
    Abrikosov, I. A.
    Theoretical study of the Mo-Ru sigma phase2008In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 32, no 1, 171-176 p.Article in journal (Refereed)
    Abstract [en]

    The thermodynamic properties of the Mo-Ru binary sigma-phase are investigated using a combination of ab initio calculations and CALPHAD modeling. Total energy calculations have been performed for the complete set of 32 end-member compounds of a 5-sublattice compound energy model. The internal crystallographic parameters for each end-member compound have been determined by minimising the total energy. A simpler, 3-sublattice model of the Mo-Ru a-phase is formulated on the basis of calculated total energies. The site occupancy is acquired by minimising the free energy given by the compound energy model. A strong preference of Mo and Ru towards high-coordination sites and icosahedral sites in the Mo-Ru a-phase is found and analysed in terms of the electronic structure.

  • 28. Grechnev, G. E.
    et al.
    Logosha, A. V.
    Svechkarev, I. V.
    Kuchin, A. G.
    Kulikov, Y. A.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eriksson, O.
    Electronic structure and magnetic properties of RNi5-xCux alloys (R=Y, La, Ce)2006In: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 32, no 12, 1140-1146 p.Article in journal (Refereed)
    Abstract [en]

    A study is made of the electronic structure and magnetic properties of RN5-xCux alloys (R = Y, La, Ce). The influence of substitution of nickel by copper on the features of the band structure and behavior of the magnetic susceptibility of these alloys is investigated. An analysis is made of the electronic states and interactions responsible for the magnetic properties of RNi5-xCux alloys.

  • 29.
    Grönhagen, Karin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Razumowski, Vsevolod
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ödqvist, J.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Phase-field coupled with CALPHAD database and ab-initio modeling of diffusion barriers and prefactors for simulating spinodal decomposition in ZrC-TiC carbidesManuscript (preprint) (Other academic)
  • 30.
    Hosseinzadeh Delandar, Arash
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Hafez Haghigha, S. M.
    Korzhavyi, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Three-dimensional dislocation dynamics simulation of plastic deformation in copper single crystalManuscript (preprint) (Other academic)
    Abstract [en]

    Dynamic deformation of single crystal copper at high strain rates ranging from 103 to 105 s-1 is modeled using three dimensional discrete dislocation dynamics method. Numerical uniaxial tensile test is performed on a model crystal along [0 0 1] orientation to examine the resulting macroscopic behavior along with microstructure evolution at high strain rates. Twenty-four straight dislocations of mixed character are randomly distributed inside a model crystal with an edge length of 1  subjected to period boundary conditions. In the simulated single crystal with the considered initial dislocation microstructure, plastic flow demonstrates a significant strain rate dependency at imposed strain rates. Rate sensitivity of flow stress observed at strain rates >> 103 s-1 agrees well with the reported experimental studies on copper single crystal.  Furthermore, strain rate considerably affects the microstructure evolution of the sample crystal as a result of influence of strain rate on dislocations generation and interactions. Formation of heterogeneous microstructure is observed at all imposed strain rates. We find that heterogeneity of microstructure escalates as strain rate increases.

  • 31.
    Hosseinzadeh Delandar, Arash
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Korzhavyi, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Investigation of loading orientation effect on dynamic deformation of single crystal copper at high strain rates: Discrete dislocation dynamics studyManuscript (preprint) (Other academic)
    Abstract [en]

    Uniaxial tensile loading of copper single crystal along [001] and [111] orientations is modeled at two high strain rates of 105 and 106 s-1. Discrete dislocation dynamics method is used to study the anisotropic characteristic of plastic deformation in the model crystal. Furthermore, strain rate sensitivity of the flow stress in copper crystal is examined. Investigation of mechanical response of single crystal to the external loading demonstrates a substantial effect of loading orientation on the plastic flow. We find that at both imposed strain rates flow stress increases significantly when tensile load is applied along [111] crystallographic axis. Similarly, plastic anisotropy is observed in dislocation density evolution such that more dislocations are generated as straining direction of single crystal is changed from [001] to [111] axis. Moreover, plastic flow behavior exhibits a profound strain rate sensitivity at both loading orientations which agrees well with experimental observations regarding strain rate dependency of flow stress in copper single crystal as strain rate exceeds 103 s-1. At both applied strain rates dislocations evolve into a heterogeneous microstructure and highest heterogeneity is observed as model crystal is loaded along [111] direction at strain rate of    106 s-1. Formation of slip bands and consequently localization of plastic deformation are detected for all considered cases. However, at the higher strain rate of 106 s-1, slip band formation is more pronounced for both loading orientations.

  • 32.
    Hugosson, Håkan Wilhelm
    et al.
    Uppsala University.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jansson, U.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Eriksson, O.
    Phase stabilities and structural relaxations in substoichiometric TiC1-x2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, no 16, 165116- p.Article in journal (Refereed)
    Abstract [en]

    First-principles calculations have been used to study the effect of vacancies and relaxation around the vacancy sites in substoichiometric TiC1-x. The effect of relaxation on phase stabilities, equilibrium volumes. and electronic structure of the substoichiometric phases was studied using a combined approach of pseudopotential plane wave and full-potential linear muffin-tin orbital methods. A relaxation away from the vacancies was found for the titanium atoms, the magnitude of which increased with vacancy concentration and the inclusion of nearest-neighbor carbon atom relaxation. The inclusion of local relaxations was found to correctly predict the off-stoichiometric equilibrium composition of titanium carbide. The anomalous volume behavior of TiC at small vacancy concentration is explained as an effect of the local relaxation of the atoms surrounding the vacancy sites, but we do not find that the lattice parameter of any of the studied stoichiometries is larger than that of ideal stoichiometric TiC.

  • 33.
    Isaev, Eyvaz
    et al.
    Moscow State Institute of Steel and Alloys.
    Baykov, Vitaly
    KTH, Superseded Departments, Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Vekilov, Yu. Kh.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Abrikosov, Igor
    Eriksson, O.
    Intrinsic defects and transition metal impurities in GaAs2004In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 272, no 3, 1961-1962 p.Article in journal (Refereed)
    Abstract [en]

    Thermodynamics of intrinsic point defects, 3d-transition metal (TM) impurities, and various defect pairs in GaAs have been studied by means of the locally self-consistent Green's function method. Antisite defects, As-Ga, are found to be the most energetically favorable defects in the As-rich GaAs. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The magnetic moments of TM impurities in the GaAs host are calculated under the assumption that orbital moments of TM are quenched and the total magnetization is due to spill ordering of electrons in the crystal. Thermodynamic possibility of formation of complexes between TM-atoms is investigated.

  • 34.
    Johansson, Börje
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Vitos, Levente
    Uppsala Universitet.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Chemical composition-elastic property maps of austenitic stainless steels2003In: Solid State Sciences, ISSN 1293-2558, Vol. 5, no 6, 931-936 p.Article in journal (Refereed)
    Abstract [en]

    Despite a tremendous development during the last decades, both as regards computer power and methodology, it has remained impossible to treat steel at a fundamental atomic level. However, recently we have shown [L. Vitos, P.A. Korzhavyi, B. Johansson, Phys. Rev. Lett. 88 (2002) 155501] that the most efficient theories of random substitutional alloys combined with advanced numerical techniques have made possible to establish a theoretical insight to the electronic structure of stainless steels. Here a detailed description of the quantum-mechanical modeling of austenitic stainless steels is presented. We adopt an ab initio electronic structure calculation method based on the coherent potential approximation, implemented within the framework of the exact muffin tin orbitals theory, to map the chemical composition distributions of austenitic stainless steels into the elastic property distributions. The so generated database can be fruitfully used in the design of new class of steel alloys.

  • 35. Kar'kin, I. N.
    et al.
    Kar'kina, L. E.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gornostyrev, Yu. N.
    Monte Carlo Simulation of the Kinetics of Decomposition and the Formation of Precipitates at Grain Boundaries of the General Type in Dilute BCC Fe-Cu Alloys2017In: Physics of the solid state, ISSN 1063-7834, E-ISSN 1090-6460, Vol. 59, no 1, 106-113 p.Article in journal (Refereed)
    Abstract [en]

    The kinetics of decomposition of a polycrystalline Fe-Cu alloy and the formation of precipitates at the grain boundaries of the material have been investigated theoretically using the atomistic simulation on different time scales by (i) the Monte Carlo method implementing the diffusion redistribution of Cu atoms and (ii) the molecular dynamics method providing the atomic relaxation of the crystal lattice. It has been shown that, for a small grain size (D similar to 10 nm), the decomposition in the bulk of the grain is suppressed, whereas the copper-enriched precipitates coherently bound to the matrix are predominantly formed at the grain boundaries of the material. The size and composition of the precipitates depend significantly on the type of grain boundaries: small precipitates (1.2-1.4 nm) have the average composition of Fe-40 at % Cu and arise in the vicinity of low-angle grain boundaries, while larger precipitates that have sizes of up to 4 nm and the average composition of Fe-60 at % Cu are formed near grain boundaries of the general type and triple junctions.

  • 36. Karkin, I. N.
    et al.
    Karkina, L. E.
    Kuznetsov, A. R.
    Petrik, M. V.
    Gornostyrev, Yu.N.
    Korzhavyi, P. A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Institute Metal Physics, Russian Federation.
    Segregation of Mg to generic tilt grain boundaries in Al: Monte Carlo modeling2015In: Materials Physics and Mechanics, ISSN 1605-2730, E-ISSN 1605-8119, Vol. 24, no 3, 201-210 p.Article in journal (Refereed)
    Abstract [en]

    The formation of equilibrium segregations at tilt grain boundaries of several different types in Al-Mg alloys has been investigated in the framework of a combined approach, which includes molecular dynamics simulation and thermodynamic Monte Carlo modeling. The concentration profile of Mg distribution in GB vicinity was calculated in dependence on the alloy concentration and temperature. We found that width of segregation on generic GB determined by feature of their structure and is match bigger in comparison with special lowenergy GB. It is shown that segregation formation is control not only energy gain due to moving solute on GB but also interaction between solute atoms; as results, maximal enrichment of GB is not exceed 25 at.%. Possible origins of the formation of extended segregation on GB in materials subjected by severe plastic deformation have been discussed.

  • 37. Karkina, L. E.
    et al.
    Karkin, I. N.
    Kuznetsov, A. R.
    Razumov, I. K.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. RAS, Inst Met Phys, Russia.
    Gornostyrev, Yu. N.
    Solute-grain boundary interaction and segregation formation in Al: First principles calculations and molecular dynamics modeling2016In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 112, 18-26 p.Article in journal (Refereed)
    Abstract [en]

    The interaction between solute atoms (Mg, Si, Ti) and grain boundaries (GBs) of different types in Al are investigated using two approaches: first principles total energy calculations and large scale atomistic simulations. We have found that both deformation (size effect) and electronic (charge transfer) mechanisms play an important role in solute-GB interaction. The deformation and electronic contributions to GB segregation energy for the considered solutes have been analyzed in dependence on the impurity and the GB type. Mg and Si atoms are calculated to segregate to GBs, while Ti atoms to repel from, GBs in Al. For the case of a symmetric special-type GB the interaction is found to be short-ranged. For a general-type GB the range of GB-solute interaction is found to be considerably longer. A method to estimate the segregation capacity of a GB has been proposed, which takes into account the solute-solute interactions, and shown to be able to correctly describe the GB enrichment in alloying elements. The features of the segregation formation in fine-grained materials produced by severe plastic deformation are discussed.

  • 38.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Monovacancy in copper: Trapping efficiency for hydrogen and oxygen impurities2014In: Computational materials science, ISSN 0927-0256, Vol. 84, 122-128 p.Article in journal (Refereed)
    Abstract [en]

    The structure and binding energy of vacancy-impurity complexes in copper are studied using first-principles calculations based on density functional theory. A single vacancy is found to be able to trap up to six hydrogen atoms which tend to be situated inside the vacancy at off-center positions (related to the octahedral interstitial positions of the ideal fcc lattice). The binding energy of an H atom dissolved in the Cu lattice (octahedral interstitial position) to a vacancy is calculated to be about 0.24 eV, practically independent of the number of H atoms already trapped by the vacancy, up to the saturation with 6 hydrogens. For an oxygen impurity in Cu, a monovacancy is shown to be a deep trap (with a binding energy of 0.95 eV). The position of a trapped O atom inside a vacancy is off-center, almost a half-way from the nearest octahedral interstitial to the vacancy center. Such a vacancy-O cluster is shown to be a deep trap for dissolved hydrogen (the calculated binding energy is 1.23 eV). The trapping results in the formation of an OH-group, where the H atom is situated near the vacancy center, and the O atom is displaced from the center along a 〈100〉 direction towards a nearby octahedral interstitial position. Further hydrogenation of the monovacancy-OH cluster is calculated to be energetically unfavourable. McNabb-Forster's equations are generalised to describe the competition between a deep hydrogen trap and a shallow one. It is demonstrated that the deep trap is almost fully filled, which explains why some of hydrogen is strongly bound and cannot be removed without vacuum treatment at elevated temperatures.

  • 39.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Magnetic models for computational thermodynamics2011In: Fundamentals of Thermodynamic Modelling of Materials, EDP Sciences, 2011, Vol. 14, 05001- p.Conference paper (Refereed)
  • 40.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Theoretical data for assessments2011In: Fundamentals of Thermodynamic Modelling of Materials, EDP Sciences, 2011, Vol. 14, 03003- p.Conference paper (Refereed)
  • 41.
    Korzhavyi, Pavel A.
    et al.
    Uppsala University.
    Abrikosov, I. A.
    Uppsala University.
    Johansson, Börje
    Uppsala University.
    Ruban, A. V.
    Technical University of Denmark.
    Skriver, H. L.
    Technical University of Denmark.
    First-principles calculations of the vacancy formation energy in transition and noble metals1999In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 59, no 18, 11693-11703 p.Article in journal (Refereed)
    Abstract [en]

    The vacancy formation energy and the vacancy formation volume of the 3d, 4d, and 5d transition and noble metals have been calculated within the local-density approximation. The calculations employ the order-N locally self-consistent Green’s-function method in conjunction with a supercell approach and include electrostatic multipole corrections to the atomic sphere approximation. The results are in excellent agreement with available full-potential calculations and with the vacancy formation energies obtained in positron annihilation measurements. The variation of the vacancy formation energy through a transition-metal series and the effects of crystal and magnetic structure are investigated and discussed.

  • 42.
    Korzhavyi, Pavel A.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Abrikosov, I. A.
    Smirnova, E. A.
    Bergqvist, L.
    Mohn, P.
    Mathieu, R.
    Svedlindh, P.
    Sadowski, J.
    Isaev, E. I.
    Vekilov, Y. K.
    Eriksson, O.
    Defect-induced magnetic structure in (Ga1-xMnx)As2002In: Physical Review Letters, ISSN 0031-9007, Vol. 88, no 18, 187202- p.Article in journal (Refereed)
    Abstract [en]

    We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga1-xMnx)As lower the total energy, compared to the case of perfect ferromagnetic ordering, when As defects on the Ga sublattice are present. Such magnetic structures are found to be stable for a range of concentrations of As antisites, and this result accounts for the observed magnetic moments and critical temperatures in (Ga1-xMnx)As . We propose an explanation for the stabilization of the partially disordered magnetic structures and conclude that the magnetization and critical temperatures should increase substantially by reducing the number of As antisite defects.

  • 43.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Thermodynamic properties of copper compounds with oxygen and hydrogen from first principles2010Report (Refereed)
    Abstract [en]

    We employ quantum-mechanical calculations (based on density functional theory and linear response theory) in order to test the mechanical and chemical stability of several solid-state configurations of Cu1+, Cu2+, O2–, H1–, and H1+ ions. We begin our analysis with cuprous oxide (Cu2O, cuprite structure), cupric oxide (CuO, tenorite structure), and cuprous hydride (CuH, wurtzite and sphalerite structures) whose thermodynamic properties have been studied experimentally. In our calculations, all these compounds are found to be mechanically stable configurations. Their formation energies calculated at T = 0 K (including the energy of zero-point and thermal motion of the ions) and at room temperature are in good agreement with existing thermodynamic data. A search for other possible solid-state conformations of copper, hydrogen, and oxygen ions is then performed. Several candidate structures for solid phases of cuprous oxy-hydride (Cu4H2O) and cupric hydride (CuH2) have been considered but found to be dynamically unstable. Cuprous oxy-hydride is found to be energetically unstable with respect to decomposition onto cuprous oxide and cuprous hydride. Metastability of cuprous hydroxide (CuOH) is established in our calculations. The free energy of CuOH is calculated to be some 50 kJ/mol higher than the average of the free energies of Cu2O and water. Thus, cuprite Cu2O is the most stable of the examined Cu(I) compounds.

  • 44.
    Korzhavyi, Pavel A.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Pourovskii, Leonid V.
    Department of Physics, Uppsala University.
    Hugosson, Håkan W.
    Department of Physics, Uppsala University.
    Ruban, Andrei V.
    Department of Physics, Technical University of Denmark.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Ab Initio Study of Phase Equilibria in TiCx2002In: Physical Review Letters, ISSN 0031-9007, Vol. 88, no 1, 015505-1-01505-4 p.Article in journal (Refereed)
    Abstract [en]

    The phase diagram for the vacancy-ordered structures in the substoichiometric TiCx (x=0.5-1.0) has been established from Monte Carlo simulations with the long-range pair and multisite effective interactions obtained from ab initio calculations. Three ordered superstructures of vacancies (Ti2C, Ti3C2, and Ti6C5) are found to be ground state configurations. Their stability has been verified by full-potential total energy calculations of the fully relaxed structures.

  • 45.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Odqvist, J.
    Nilsson, J.-O.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Electronic structure and effective chemical and magnetic exchange interactions in bcc Fe-Cr alloys2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 5, 054202- p.Article, review/survey (Refereed)
    Abstract [en]

    Electronic structure calculations are employed in order to investigate the cohesive properties (lattice parameter, enthalpy of formation, and bulk modulus) of random Fe-Cr alloys as a function of composition and magnetic state, as well as to derive the chemical and magnetic exchange interactions of the constituent atoms. The calculations predict certain anomalies in the cohesive properties of ferromagnetic alloys at a concentration of about 7 at % Cr; these anomalies may be related to the changes in Fermi-surface topology that occur with composition in this alloy system. The obtained interatomic interactions are used as parameters in the configurational (Ising) and magnetic (Heisenberg) Hamiltonians for modeling finite-temperature thermodynamic properties of the alloys. We discuss the approximations and limitations of similar modeling approaches, investigate the origin of existing difficulties, and analyze possible ways of extending the theoretical models in order to capture the essential physics of interatomic interactions in the Fe-Cr or similar alloys where magnetism plays a crucial role in the phase stability.

  • 46.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles calculations as a new tool in steel research2008In: 6th European Stainless Steel Conference, Science and Market Helsinki, Finland, June 10-13, 2008: Proceedings / [ed] P. Karjalainen and S. Hertzman, Jernkontoret , 2008, 279-284 p.Conference paper (Refereed)
    Abstract [en]

    Great scepticism over the earliest applications of the first-principles theory to the calculation of the ground state properties of real systems in the 70’s and 80’s has gradually turned into a widespread belief in its quantitative accuracy and predictive power, due to a great number of successful applications to very different systems and problems, so that several leading materials manufacturing companies have initiated first-principles based research programs aimed at design of new materials. However, the role of first-principles calculations in the design process, and, most importantly, their potential, remain quite obscure. We therefore try to give a “balanced” view on the possibilities of first-principles calculations, not only telling success stories, but also discussing their problems and limitations. Then, we demonstrate uniqueness of the information that can be obtained using first-principles methods. Thus we determine their place among the traditional research methods and tools in materials science. In order to show the capabilities of first-principles calculations, we present some recent applications of first-principles methods to investigation of the thermodynamic and kinetic properties of austenitic (including high-nitrogen) and ferritic steels, at the atomic level. Finally, we indicate problems, related to steel research and development, where first-principles methods (together with other experimental or theoretical techniques) can lead to substantial progress or even breakthroughs.

  • 47.
    Korzhavyi, Pavel A.
    et al.
    Uppsala University.
    Ruban, Andrei V.
    Technical University of Denmark.
    Lozovoi, A. Y.
    Vekilov, Y. K.
    Abrikosov, I. A.
    Johansson, Börje
    Uppsala University.
    Constitutional and thermal point defects in B2 NiAl2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 9, 6003-6018 p.Article in journal (Refereed)
    Abstract [en]

    The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects (antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively) are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.

  • 48.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    First-principles evaluation of the effect of alloying elements on the lattice parameter of a 23Cr25NiWCuCo austenitic stainless steel to model solid solution hardening contribution to the creep strength2015In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 626, 213-219 p.Article in journal (Refereed)
    Abstract [en]

    By the use of first-principles calculations based on density functional theory, lattice misfit parameters for alloying elements in the austenitic stainless steel 23Cr25NiWCuCo have been derived. These lattice misfit parameters have been applied to determine the solid solution hardening of the elements W, Nb, and Cu in the steel. The model for solid solution hardening is based on work by Hirth and Lothe, where solutes are creating Cottrell clouds around the dislocations and slow down their motion. The model is also verified by comparison to creep tests for Ni-20%Cr and Ni-20%Cr-6W, where W is almost completely in solid solution and no other strengthening mechanism than solid solution hardening should be active. The contribution from the interstitial elements C and N to the solid solution hardening is found to be negligibly small for the studied steel.

  • 49.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Soroka, Inna
    Uppsala Universitet.
    Boman, Mats
    Uppsala Universitet.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Thermodynamics of stable and metastable Cu-O-H compounds2011Conference paper (Refereed)
    Abstract [en]

    We apply density functional perturbation theory together with experimental studies in order to investigate the structure and physical properties of possible stable and metastable copper(I) compounds with oxygen and hydrogen. Copper(I) hydride, CuH, is found to be a metastable phase which decomposes at ambient conditions and exhibiting a semiconducting gap in the electronic spectrum. The calculated structure and phonon spectra are found to be in good agreement with experimental data. The phonon spectra of a novel metastable phase, copper(I) hydroxide, are also determined.

  • 50.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Isaev, Eyvaz I.
    Lilja, Christina
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Exploring monovalent copper compounds with oxygen and hydrogen2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 3, 686-689 p.Article in journal (Refereed)
    Abstract [en]

    New important applications of copper metal, e.g., in the areas of hydrogen production, fuel cell operation, and spent nuclear fuel disposal, require accurate knowledge of the physical and chemical properties of stable and metastable copper compounds. Among the copper(I) compounds with oxygen and hydrogen, cuprous oxide Cu(2)O is the only one stable and the best studied. Other such compounds are less known (CuH) or totally unknown (CuOH) due to their instability relative to the oxide. Here we combine quantum-mechanical calculations with experimental studies to search for possible compounds of monovalent copper. Cuprous hydride (CuH) and cuprous hydroxide (CuOH) are proved to exist in solid form. We establish the chemical and physical properties of these compounds, thereby filling the existing gaps in our understanding of hydrogen- and oxygen-related phenomena in Cu metal.

123 1 - 50 of 105
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