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  • 1. Abrikosov, I. A.
    et al.
    Kissavos, A. E.
    Liot, F.
    Alling, B.
    Simak, S. I.
    Peil, O.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Competition between magnetic structures in the Fe rich fcc FeNi alloys2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 1Article in journal (Refereed)
    Abstract [en]

    We report on the results of a systematic ab initio study of the magnetic structure of Fe rich fcc FeNi binary alloys for Ni concentrations up to 50 at. %. Calculations are carried out within density-functional theory using two complementary techniques, one based on the exact muffin-tin orbital theory within the coherent potential approximation and another one based on the projector augmented-wave method. We observe that the evolution of the magnetic structure of the alloy with increasing Ni concentration is determined by a competition between a large number of magnetic states, collinear as well as noncollinear, all close in energy. We emphasize a series of transitions between these magnetic structures, in particular we have investigated a competition between disordered local moment configurations, spin spiral states, the double layer antiferromagnetic state, and the ferromagnetic phase, as well as the ferrimagnetic phase with a single spin flipped with respect to all others. We show that the latter should be particularly important for the understanding of the magnetic structure of the Invar alloys.

  • 2. Abrikosov, I. A.
    et al.
    Ponomareva, A. V.
    Barannikova, S. A.
    Hellman, O.
    Vekilova, O.Yu.
    Simak, S. I.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Multiscale approach to theoretical simulations of materials for nuclear energy applications: Fe-Cr and Zr-based alloys2013In: Advances in materials for nuclear energy: symposium held November 25-30, Boston, Massachusetts, U.S.A., Materials Research Society, 2013, 3-14 p.Conference paper (Refereed)
    Abstract [en]

    We review basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of alloys. We concentrate on methods that allow for an efficient treatment of compositional and thermal disorder effects. In particular, we present novel approach to evaluate free energy for strongly anharmonic systems. Theoretical tools are then employed in studies of two materials systems relevant for nuclear energy applications: Fe-Cr and Zr-based alloys. In particular, we investigate the effect of hydrostatic pressure and multicomponent alloying on the mixing enthalpy of Fe-Cr alloys, and show that in the ferromagnetic state both of them reduce the alloy stability at low Cr concentration. For Zr-Nb alloys, we demonstrate how microscopic parameters calculated from first-principles can be used in higher-level models.

  • 3. Alling, B.
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Abrikosov, I. A.
    Effect of thermal expansion, electronic excitations, and disorder on the Curie temperature of Ni1-xCuxMnSb alloys2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 13Article in journal (Refereed)
    Abstract [en]

    We demonstrate the importance of thermal effects such as temperature-induced electronic, magnetic and vibrational excitations, as well as structural defects in the first-principles calculations of the magnetic critical temperature of complex alloys using half-Heusler Ni1-xCuxMnSb alloys as a case study. The thermal lattice expansion and one-electron excitations have been accounted for self-consistently in the Curie temperature calculations. In the Ni-rich region, electronic excitations, thermal expansion, and structural defects substantially decrease the calculated Curie temperature. At the same time, some defects are shown to increase T-C in Cu-rich samples.

  • 4. Alling, B.
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Karimi, A.
    Hultman, L.
    Abrikosov, I. A.
    Unified cluster expansion method applied to the configurational thermodynamics of cubic Ti1-xAlxN2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 10, 104203- p.Article in journal (Refereed)
    Abstract [en]

    We study the thermodynamics of cubic Ti1-xAlxN using a unified cluster expansion approach for the alloy problem. The purely configurational part of the alloy Hamiltonian is expanded in terms of concentration- and volume-dependent effective cluster interactions. By separate expansions of the chemical fixed lattice, and local lattice relaxation terms of the ordering energies, we demonstrate how the screened generalized perturbation method can be fruitfully combined with a concentration-dependent Connolly-Williams cluster expansion method. Utilizing the obtained Hamiltonian in Monte Carlo simulations we access the free energy of Ti1-xAlxN alloys and construct the isostructural phase diagram. The results show striking similarities with the previously obtained mean-field results: The metastable c-TiAlN is subject to coherent spinodal decomposition over a larger part of the concentration range, e.g., from x >= 0.33 at 2000 K.

  • 5. Alling, B.
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Karimi, A.
    Peil, O. E.
    Simak, S. I.
    Hultman, L.
    Abrikosov, I. A.
    Mixing and decomposition thermodynamics of c-Ti1-xAlxN from first-principles calculations2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 4Article in journal (Refereed)
    Abstract [en]

    We describe an efficient first-principles method that can be used to calculate mixing enthalpies of transition metal nitrides with B1 structure and substitutional disorder at the metal sublattice. The technique is based on the density functional theory. The independent sublattice model is suggested for the treatment of disorder-induced local lattice relaxation effects. It supplements the description of the substitutional disorder within the coherent potential approximation. We demonstrate the excellent accuracy of the method by comparison with calculations performed by means of the projector augumented wave method on supercells constructed as special quasirandom structures. At the same time, the efficiency of the technique allows for total energy calculations on a very fine mesh of concentrations which enables a reliable calculation of the second concentration derivative of the alloy total energy. This is a first step towards first-principles predictions of concentrations and temperature intervals where the alloy decomposition proceeds via the spinodal mechanism. We thus calculate electronic structure, lattice parameter, and mixing enthalpies of the quasibinary alloy c-Ti1-xAlxN. The lattice parameter follows Vegard's law at low fractions of AlN but deviates increasingly with increasing Al content. We show that the asymmetry of the mixing enthalpy and its second concentration derivative is associated with substantial variations of the electronic structure with alloy composition. The phase diagram is constructed within the mean-field approximation.

  • 6. Bergman, Anders
    et al.
    Burkert, Till
    Sanyal, Biplab
    Frota-Pessoa, Sonia
    Nordstrom, Lars
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Simak, Sergei I.
    Eriksson, Olle
    Magnetic properties of Fe/Co(001) superlattices from first-principles theory2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 17Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of Fe/Co(001) superlattices have been studied using fully-relativistic first-principles theories. The average magnetic moment shows a behavior similar to bulk Fe-Co alloys, i.e., an enhanced magnetic moment for low Co concentrations, as described by the Slater-Pauling curve. The maximum of the magnetization curve, however, is lowered and shifted towards the Fe-rich compositions. The increased average magnetic moment for the Fe-rich superlattices, compared to bulk Fe, is due to an enhancement of the Fe spin moment close to the Fe-Co interface. The orbital moments were found to be of the same size as in bulk. The effect of interface roughness on the magnetic properties was investigated, and it was found that-despite local fluctuations due to the varying coordination-the average magnetic moment is only slightly affected. From a mapping of first-principles interactions onto the screened generalized perturbation method, we calculate the temperatures for when Fe/Co superlattices break up into an alloy configuration. Furthermore, the tetragonal distortion of the superlattice structure was found to only have a minor effect on the magnetic moments. Also, the calculated easy axis of magnetization is in the film plane for all compositions studied. It lies along the [100] direction for Fe-rich superlattices and along the [110] direction for Co-rich compositions. The transition of the easy axis occurs around a Co concentration of 50%.

  • 7. Blanter, M. S.
    et al.
    Dmitriev, V. V.
    Mogutnov, B. M.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Interaction of interstitial atoms and configurational contribution to their thermodynamic activity in V, Nb, and Ta2017In: Physics of metals and metallography, ISSN 0031-918X, E-ISSN 1555-6190, Vol. 118, no 2, 105-112 p.Article in journal (Refereed)
    Abstract [en]

    The pairwise interaction energies of O–O and N–N in bcc metals of group VB, which were calculated earlier using first-principles methods, have been employed to analyze the effect of the interatomic interactions on the configurational contribution to the thermodynamic activity. The strong effect of interstitial- interstitial interaction has been shown. The configurational contribution grows in the row (Nb–N) → (V–N) → (Ta–N) → (Nb–O) → (V–O) → (Ta–O), which is caused by a weakening of the mutual attraction of interstitial atoms in these solid solutions. The strong repulsion that characterizes the majority of coordination shells only weakly affects the thermodynamic activity. The character of the temperature dependence of the configurational contribution is defined by the strength of the mutual attraction of the interstitial atoms, i.e., upon strong attraction, the contribution increases with increasing temperature (Nb–N, V–N, Ta–N, and Nb–O) and, upon weak attraction, it decreases (V–O and Ta–O).

  • 8. Blanter, M. S.
    et al.
    Dmitriev, V. V.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio Based O-O Investigation and the Snoek Relaxation in Nb-O2012In: Diffusion and Defect Data Pt.B: Solid State Phenomena, Trans Tech Publications Inc., 2012, Vol. 184, 63-68 p.Conference paper (Refereed)
    Abstract [en]

    It is common knowledge that interstitial-interstitial interaction influence on the Snoek relaxation. We used a computer simulation of this effect in the Nb-O alloy to test the adequacy of various models of the O-O interaction and clarify the mechanism of this effect The energy calculations in the first twelve coordination shells have been performed by the projector augmentedwave (PAW) method as implemented in the Vienna ab initio simulation package (VASP). The energies have been calculated in different ways which vary in the method of determination the energy of non-interacting O-O pairs. The energies calculated on the various variants are similar but in one case there is O-O repulsion in all first twelve coordination shells, whereas in another one can see attraction in four of twelve shells. Internal friction Q -1 was calculated as a sum of the contributions from individual interstitial atoms in different environments, each of which being assumed to be the Debye function. It is assumed that long-range interaction of oxygen atoms affects the distribution of these atoms and the energy of each interstitial atom in the octahedral interstices before a jump and after a jump. The Monte Carlo method is used for simulating short-range order of interstitial atoms and for calculating values of energy changes. Comparison of the calculated temperature and concentration dependence of the Snoek peak with the published data showed that the PAW supercell calculation of the O-O interactions in Nb describes the behavior of the interstitial solid solution adequately. It proves also that the impact of interstitial atom concentration on the Snoek relaxation is connected to the mutual attraction of these atoms.

  • 9. Blanter, M. S.
    et al.
    Dmitriev, V. V.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Interstitial-interstitial interactions in bcc VB group metals: Ab initio calculations2013In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 74, no 5, 716-722 p.Article in journal (Refereed)
    Abstract [en]

    Chemical and strain-induced interactions of oxygen and nitrogen interstitials in bcc V and Ta have been obtained for the first 12 coordination shells in the supercell first-principles calculations by the Viena ab initio simulation package (VASP). It is shown that the chemical interactions are dominating at the first several coordination shells while the strain-induced interactions become important at more distant coordination shells. The latter are in reasonable agreement with the earlier results of a microscopic phenomenological Krivoglaz-Kanzaki-Khachaturyan model (KKKM). The obtained interstitial-interstitial interactions have been used in calculations of the concentration dependence of the oxygen Snoek peak, which is in good agreement with the existing experimental data.

  • 10. Blanter, M. S.
    et al.
    Dmitriev, V. V.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Ordering in V-O and V-N solid solutions: Computer simulation2014In: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 78, no 10, 1030-1034 p.Article in journal (Refereed)
    Abstract [en]

    The atomic structures of interstitial solid solutions O and N in V at relatively low concentrations O(N)/V = 1/16 or 1/8 are calculated using the Monte Carlo method. A combined model of long-range interaction between interstitial atoms is employed. The first 12 shells contain ab initio energies and the energies in shells 13–18 are calculated on the basis of a phenomenological model of deformation interaction. The ordered solid solutions are long-period structures with body-centered tetragonal crystal lattices and tetragonality c/a < 1.

  • 11.
    Blanter, M. S.
    et al.
    Moscow State University of Instrumental Engineering and Information Science, Department of Nanomaterials.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Dmitriev, V. V.
    Moscow State University of Instrumental Engineering and Information Science, Department of Nanomaterials.
    Strain-induced interaction of interstitials in IVA group hcp metals2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 10, 1416-1420 p.Article in journal (Refereed)
    Abstract [en]

    Strain-induced (elastic) interactions of oxygen, nitrogen and carbon atoms in IVA group metals, alpha-Ti, Zr, and -Hf, are calculated in the framework of the microscopic Krivoglaz-Kanzaki-Khachaturyan theory. The experimental elastic constants, lattice spacing of the host metal, and concentration expansion coefficients are used as the input numerical parameters. The resulting interactions are stronger in a-Ti than in alpha-Zr and alpha-Hf. A comparative analysis of interactions in the hcp IVA group metals with those in bcc and fcc solid solutions reveals the crystal structure effect. In general, the strain-induced interactions of O, N, and C in hcp IVA group metals are weaker than in bcc solid solutions and are stronger than in fcc solid solutions.

  • 12. Bleskov, I.
    et al.
    Hickel, T.
    Neugebauer, J.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Impact of local magnetism on stacking fault energies: A first-principles investigation for fcc iron2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 21, 214115Article in journal (Refereed)
    Abstract [en]

    A systematic ab initio study of the influence of local magnetism on the generalized stacking fault energy (GSFE) surface in pure fcc iron at 0 K has been performed. In the calculations we considered ferro- and antiferro-(single- and double-layer) magnetic order of local moments as well as their complete disorder, corresponding to paramagnetic (PM) state. We have shown that local magnetism is one of the most important factors stabilizing austenitic structure in iron (with respect to more stable at 0 K hcp) and that the perturbation of magnetic structure by the formation of stacking fault is a short-range effect. Local magnetism also strongly influences the GSFE surface topology and, therefore, the material's plasticity by reducing the energetic barriers that need to be overcome to form the intrinsic stacking fault (ISF) or return from the ISF structure to fcc. The influence of atomic relaxations on such barriers is moderate and does not exceed 15%. In addition, a methodology to evaluate the PM ISF energy using a superposition of the ISF energies obtained for ordered magnetic structures is proposed to overcome computational impediments arising when dealing with disorder in the PM state. The complications of the proposed methodology together with the ways to overcome them are also discussed.

  • 13. Bligaard, T.
    et al.
    Johannesson, G. H.
    Ruban, Andrei V.
    Skriver, H. L.
    Jacobsen, K. W.
    Norskov, J. K.
    Pareto-optimal alloys2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 22, 4527-4529 p.Article in journal (Refereed)
    Abstract [en]

    Large databases that can be used in the search for new materials with specific properties remain an elusive goal in materials science. The problem is complicated by the fact that the optimal material for a given application is usually a compromise between a number of materials properties and the cost. In this letter we present a database consisting of the lattice parameters, bulk moduli, and heats of formation for over 64 000 ordered metallic alloys, which has been established by direct first-principles density-functional-theory calculations. Furthermore, we use a concept from economic theory, the Pareto-optimal set, to determine optimal alloy solutions for the compromise between low compressibility, high stability, and cost.

  • 14. Bochkarev, A. S.
    et al.
    Zamulko, S. O.
    Gorbatov, O. I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sidorenko, S. I.
    Puschnig, P.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A single-volume approach for vacancy formation thermodynamics calculations2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 116, no 1, 16001Article in journal (Refereed)
    Abstract [en]

    The vacancy formation Gibbs free energy, enthalpy and entropy in fcc Al, Ag, Pd, Cu, and bcc Mo are determined by first-principles calculations using the quasi-harmonic approximation to account for vibrational contributions. We show that the Gibbs free energy can be determined with sufficient accuracy in a single-volume approach using the fixed equilibrium volume of the defect-free supercell. Although the partial contributions to the Gibbs free energy, namely, the formation enthalpy and entropy exhibit substantial errors when obtained directly in this approach, they can be computed from the Gibbs free energy using the proper thermodynamic relations. Compared to experimental data, the temperature dependence of the vacancy formation Gibbs free energy is accounted for at low temperatures, while it overestimates the measurements at high temperature, which is attributed to the neglect of anharmonic effects.

  • 15. Bogdanov, V. I.
    et al.
    Popov, V. A.
    Portnoi, V. K.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Chemical and deformational interactions in solid solution of carbon in nickel2012In: Physics of metals and metallography, ISSN 0031-918X, Vol. 113, no 9, 831-835 p.Article in journal (Refereed)
    Abstract [en]

    A first-principles stuy of ordering phenomena in hcp interstitial solid solutions of oxygen and nitrogen in Ti, Zr and Hf has demonstrated that the dominant contributions to the interaction energy of interstitial atoms are of chemical nature; thus, it is necessary to modify the previously established concepts about the priority role of deformational interactions in interstitial solutions. We have continued studies of the role of chemical and deformational interactions of interstitial atoms by the example of solid solutions of carbon in nickel. The results obtained also confirm a significant role of chemical interactions between carbon atoms in these solid solutions. The results were compared with the experimental data on the enthalpy of carbon dissolution in nickel and on the coefficient of solutal expansion of the lattice.

  • 16. Bogdanov, V. I.
    et al.
    Popov, V. A.
    Portnoi, V. K.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles investigations of interatomic interactions in Ni3Al alloyed by interstitial and substitutional impurities2013In: Physics of metals and metallography, ISSN 0031-918X, Vol. 114, no 3, 191-196 p.Article in journal (Refereed)
    Abstract [en]

    First-principles calculations of the total energy of interstitial and substitutional solid solutions in intermetallic compound Ni3Al were performed based on methods using Vienna ab-initio simulation package (VASP). The results of the calculations for interstitial solutions of carbon in Ni3Al confirmed the priority role of chemical interactions over deformational ones for the nearest neighbors. We attempted to use first-principles methods of calculation of the deformation interaction and continuum approaching in the theory of solutions to calculate coefficients of the concentration changes of the lattice spacing. Comparison of the calculation results with experimental data of substitutional impurities in Ni3Al has shown that the proposed method can aid in the study of the distribution of impurity atoms on the sublattices of the ordered phases, intermetallic compounds. We have proposed a method of calculating the partial molar volume of impurity in interstitial solid solutions.

  • 17. Bogdanov, V. I.
    et al.
    Popov, V. A.
    Portnoi, V. K.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Method for calculating coefficients of concentrational variations in lattice constants and the distribution of impurity atoms between sublattices in intermetallic compounds2013In: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 77, no 11, 1360-1362 p.Article in journal (Refereed)
    Abstract [en]

    A method is proposed for calculating coefficients of concentrational variations in lattice constants in solid solutions, based on first-principles determination of the total energy of solid solutions and the continual approximation in the solutions theory, allowing for the deformation interaction of impurity atoms due to distortions of the solvent crystal lattice.

  • 18. Breidi, A.
    et al.
    Fries, S. G.
    Palumbo, M.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Materials Center Leoben Forschung GmbH, Leoben, Austria.
    First-principles modeling of energetic and mechanical properties of Ni-Cr, Ni-Re and Cr-Re random alloys2016In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 117, 45-53 p.Article in journal (Refereed)
    Abstract [en]

    We apply the exact-muffin-tin-orbitals (EMTO) method to investigate structural properties, formation enthalpies, mechanical stability and polycrystalline moduli in Ni-Re, Ni-Cr and Cr-Re disordered fcc, bcc and hcp phases. Substitutional disorder is treated by using the coherent potential approximation (CPA). We predict the alloy lattice parameters in good agreement with the experiment. We find a continuous softening, as a function of Cr composition, of the tetragonal shear modulus C' in fcc Ni-Cr phase indicating mechanical instability in Cr-rich Ni-Cr alloys. On the other hand, we show that the mechanical stability of fcc Ni-Re alloys persists through the whole composition range. We observe an intriguing behaviour of the Young's modulus vs. the intrinsic ductility curve in Ni-rich Ni-Re fcc phase.

  • 19. Breidi, A.
    et al.
    Fries, S. G.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. School of Metallurgy and Materials, University of Birmingham, United Kingdom.
    Ideal compressive strength of fcc Co, Ni, and Ni-rich alloys along the (001) direction: A first-principles study2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, no 14, 144106Article in journal (Refereed)
    Abstract [en]

    We perform density functional theory based first-principles calculations to identify promising alloying elements (X) capable of enhancing the compressive uniaxial theoretical (ideal) strength of the fcc Ni-matrix along the 001 direction. The alloying element belongs to a wide range of 3d,4d, and 5d series with nominal composition of 6.25 at. %. Additionally, a full elastic study is carried to investigate the ideal strength of fcc Ni and fcc Co. Our results indicate that the most desirable alloying elements are those with half d-band filling, namely, Os, Ir, Re, and Ru.

  • 20. Burkert, T.
    et al.
    Eriksson, O.
    Simak, S. I.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Sanyal, B.
    Nordstrom, L.
    Wills, J. M.
    Magnetic anisotropy of L1(0) FePt and Fe1-xMnxPt2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 13Article in journal (Refereed)
    Abstract [en]

    The uniaxial magnetic anisotropy energy (MAE) of L1(0) FePt and Fe1-xMnxPt, x=0-0.25, was studied from first principles using two fully relativistic computational methods, the full-potential linear muffin-tin orbitals method and the exact muffin-tin orbitals method. It was found that the large MAE of 2.8 meV/f.u. is caused by a delicate interaction between the Fe and Pt atoms, where the large spin-orbit coupling of the Pt site and the hybridization between Fe 3d and Pt 5d states is crucial. The effect of random order on the MAE was modeled by mutual alloying of the sublattices within the coherent potential approximation (CPA), and a strong dependence of the MAE on the degree of chemical long-range order was found. The alloying of FePt with Mn was investigated with the virtual crystal approximation and the CPA as well as supercell calculations. The MAE increases up to 33% within the concentration range studied here, an effect that is attributed to band filling. Furthermore, the dependence of the MAE on the structural properties was studied.

  • 21. Christoffersen, E.
    et al.
    Liu, P.
    Ruban, Andrei V.
    Skriver, H. L.
    Norskov, J. K.
    Anode materials for low-temperature fuel cells: A density functional theory study2001In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 199, no 1, 123-131 p.Article in journal (Refereed)
    Abstract [en]

    Based on density functional calculations, we discuss the effect of alloying Pt with other metals for use as anode catalyst materials in low-temperature fuel cells. We discuss why a few parts per million of CO in the H-2 fuel can poison Pt surfaces and how this problem can be alleviated by alloying, and an extensive data base of the effect of alloying on the reactivity that includes all binary combinations of the transition metals to the right in the periodic table is given. We also discuss the effect of surface segregation and give a calculated data base of segregation energies of binary transition metal alloys. Based on extensive Monte Carlo simulations we show that while the adsorbate-free surface of a Ru0.5Pt0.5 alloy has no Ru in the first layer, the presence of CO can move some Ru to the surface, but all these Ru atoms are covered by CO.

  • 22. Dmitriev, V. V.
    et al.
    Blanter, M. S.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Interaction of interstitial nitrogen atoms in Nb: Ab initio calculations2012In: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 76, no 1, 1-6 p.Article in journal (Refereed)
    Abstract [en]

    Ab initio calculations of pair nitrogen interstitials interaction in the first 12 coordination shells of a Nb crystal lattice are performed using the Vienna ab initio simulation package (VASP), and chemical and strain-induced contributions are analyzed. It is shown that rapidly decreasing chemical repulsion prevails in the nearest coordination shells, whereas strain-induced (elastic) interaction makes the main contribution in more distant shells.

  • 23. Dmitriev, V. V.
    et al.
    Blanter, M. S.
    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.
    Ab initio based investigation of interstitial interactions and Snoek relaxation in Nb-O2012In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 73, no 2, 182-187 p.Article in journal (Refereed)
    Abstract [en]

    Chemical and strain-induced effective pair interactions of interstitial oxygen atoms in bcc Nb have been determined in supercell first-principles calculations using Vienna ab initio simulation package (VASP). The strain-induced interactions are in reasonable agreement with those obtained earlier within a phenomenological microscopic Krivoglaz-Kanzaki-Khachaturyan model (KKKM). At the same time, the chemical interactions, which have been considered to be small in earlier theoretical considerations, turned out to be dominating at the first several coordination shells. The obtained interactions have been used in calculations of the concentration- and temperature-dependence of the internal friction Snoek peak. The theoretical results are found to be in good agreement with the existing experimental data.

  • 24. Duong, T. C.
    et al.
    Hackenberg, R. E.
    Volz, H. M.
    Llobet, A.
    Smith, A. I.
    King, G.
    Landa, A.
    Gibbons, S.
    Bajaj, S.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Turchi, P. E. A.
    Arroyave, R.
    A hierarchical computational thermodynamic and kinetic approach to discontinuous precipitation in the U-Nb system2015In: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, International Conference on Solid-Solid Phase Transformations in Inorganic Materials , 2015, 887-894 p.Conference paper (Refereed)
    Abstract [en]

    U-Nb alloys decompose via discontinuous precipitation (DP) over a broad range of aging conditions, adversely affecting their properties. The growth kinetics, lamellar spacing, and Nb partitioning have been measured, but the thermodynamic and kinetic factors underlying these specific transformation characteristics and reaction paths, vis-a-vis the monotectoid reaction, are not fully resolved. In this work, a hierarchical computational thermodynamic and kinetic approach was carried out to investigate DP. The hierarchical approach started with density-functional theory (DFT) investigations of ground-state formation energies of bcc-based U-Nb alloys. The estimated energetic data was then utilized as an imposed first-principles-based constraint to improve the consistency of the CALPHAD thermodynamic and, subsequently, kinetic assessments of U-Nb. Phasefield simulations were then carried out to study DP's microstructure evolution using the assessed CALPHAD thermodynamic and kinetic representations. Good agreement with experiments on different physical/length scales was achieved, which validates the present theoretical contributions to a better understanding of DP in U-Nb alloys.

  • 25. Ekholm, M.
    et al.
    Zapolsky, H.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vernyhora, I.
    Ledue, D.
    Abrikosov, I. A.
    Influence of the Magnetic State on the Chemical Order-Disorder Transition Temperature in Fe-Ni Permalloy2010In: Physical Review Letters, ISSN 0031-9007, Vol. 105, no 16, 167208- p.Article in journal (Refereed)
    Abstract [en]

    In magnetic alloys, the effect of finite temperature magnetic excitations on phase stability below the Curie temperature is poorly investigated, although many systems undergo phase transitions in this temperature range. We consider random Ni-rich Fe-Ni alloys, which undergo chemical order-disorder transition approximately 100 K below their Curie temperature, to demonstrate from ab initio calculations that deviations of the global magnetic state from ideal ferromagnetic order due to temperature induced magnetization reduction have a crucial effect on the chemical transition temperature. We propose a scheme where the magnetic state is described by partially disordered local magnetic moments, which in combination with Heisenberg Monte Carlo simulations of the magnetization allows us to reproduce the transition temperature in good agreement with experimental data.

  • 26. Engelke, M.
    et al.
    Schönfeld, B.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Near-surface microstructure of Ni-23 at. % Pt: Grazing incidence diffraction and first-principles calculations2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 5, 054205- p.Article in journal (Refereed)
    Abstract [en]

    Diffuse x-ray scattering under grazing incidence was measured of a Ni-23.2 at. % Pt(110) surface at 923 K. The modulation of in-plane and out-of-plane scattering is characterized by the maxima in short-range order scattering located at positions of the X type (as for the bulk microstructure). The Warren-Cowley short-range order parameters from diffuse scattering are in good agreement with theoretical simulations based on bulk effective pair interaction parameters from first-principles theory. The nearest-neighbor interaction parameter is dominant also when determined from short-range order scattering. Its value is larger than for the bulk microstructure of Pt-rich alloys, what might reflect the difference in composition and is not compellingly due to the near-surface microstructure. Allowing for the presence of a tetragonal site occupation, indications for a segregation profile are weak in diffuse scattering and hardly resolvable for the Warren-Cowley short-range order parameters. This is consistent with the findings for layer-resolved short-range order parameters from theory. Theoretical simulations also demonstrated that the strong Ni enrichment of the surface layer has the same origin as the segregation reversal for the (110) surface in the case of Ni-50 at. % Pt.

  • 27. Glazyrin, K.
    et al.
    Pourovskii, L. V.
    Dubrovinsky, L.
    Narygina, O.
    McCammon, C.
    Hewener, B.
    Schuenemann, V.
    Wolny, J.
    Muffler, K.
    Chumakov, A. I.
    Crichton, W.
    Hanfland, M.
    Prakapenka, V. B.
    Tasnadi, F.
    Ekholm, M.
    Aichhorn, M.
    Vildosola, V.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Katsnelson, M. I.
    Abrikosov, I. A.
    Importance of Correlation Effects in hcp Iron Revealed by a Pressure-Induced Electronic Topological Transition2013In: Physical Review Letters, ISSN 0031-9007, Vol. 110, no 11, 117206- p.Article in journal (Refereed)
    Abstract [en]

    We discover that hcp phases of Fe and Fe0.9Ni0.1 undergo an electronic topological transition at pressures of about 40 GPa. This topological change of the Fermi surface manifests itself through anomalous behavior of the Debye sound velocity, c/a lattice parameter ratio, and Mossbauer center shift observed in our experiments. First-principles simulations within the dynamic mean field approach demonstrate that the transition is induced by many-electron effects. It is absent in one-electron calculations and represents a clear signature of correlation effects in hcp Fe.

  • 28. Gorbatov, O. I.
    et al.
    Gornostyrev, Y. N.
    Kuznetsov, A. R.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Effect of magnetism on short-range order formation in Fe-Si and Fe-Al alloys2011In: International Conference on Solid-Solid Phase Transformations in Inorganic Materials, PTM 2010, 2011, 618-623 p.Conference paper (Refereed)
    Abstract [en]

    Short-range order formation in dilute Fe-Si and Fe-Al alloys has been investigated by statistical Monte Carlo simulations with effective interactions deduced from first principles calculations for different magnetic structures of bcc Fe. We find that the variation of the magnetic order from ferromagnetic to paramagnetic leads to significant changes in effective cluster interactions and, as follow, in short-range order parameters of alloys. It is shown in agreement with experiment the B2 type short-range order is formed above the Curie temperature, TC, while the D03 type short-range order is preferred below TC.

  • 29.
    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.

  • 30. 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.

  • 31. 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.

  • 32. Gorbatov, O. I.
    et al.
    Kuznetsov, A. R.
    Gornostyrev, Yu. N.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ershov, N. V.
    Lukshina, V. A.
    Chernenkov, Yu. P.
    Fedorov, V. I.
    Role of Magnetism in the Formation of a Short-Range Order in Iron-Silicon Alloys2011In: Journal of Experimental and Theoretical Physics, ISSN 1063-7761, E-ISSN 1090-6509, Vol. 112, no 5, 848-859 p.Article in journal (Refereed)
    Abstract [en]

    The formation of a short-range order in soft magnetic Fe-Si alloys depending on the annealing temperature has been investigated theoretically and experimentally. The B2-type short-range order has been observed in samples quenched from temperatures T > T(C) (where T(C) is the Curie temperature) with the content c(Si) close to the boundary of the two-phase region. Annealing at temperatures T < T(C) for the content c(Si) >= 0.08 leads to an increase in the fraction of regions with the D0(3)-type short-range order. The mechanism of the formation of the short-range order in Fe-Si solid solutions has been analyzed by the Monte Carlo simulation with the ab initio calculated interatomic interaction parameters. It has been shown that the energy of the effective Si-Si interaction in bcc iron strongly depends on the magnetic state of the matrix. As a result, the B2-type short-range order is formed at T > T(C) and is fixed at quenching, whereas the D0(3)-type short-range order is equilibrium in the ferromagnetic state. The results reveal the decisive role of magnetism in the formation of the short-range order in Fe-Si alloys and allow the explanation of the observed structural features of the alloys depending on the composition and temperature.

  • 33. 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.

  • 34.
    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.

  • 35.
    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.

  • 36.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lomaev, I. L.
    Gornostyrev, Yu. N.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Furrer, D.
    Venkatesh, V.
    Novikov, D. L.
    Burlatsky, S. F.
    Effect of composition on antiphase boundary energy in Ni3Al based alloys: Ab initio calculations2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 22, 224106Article in journal (Refereed)
    Abstract [en]

    The effect of composition on the antiphase boundary (APB) energy of Ni-based L1(2)-ordered alloys is investigated by ab initio calculations employing the coherent potential approximation. The calculated APB energies for the {111} and {001} planes reproduce experimental values of the APB energy. The APB energies for the nonstoichiometric gamma' phase increase with Al concentration and are in line with the experiment. The magnitude of the alloying effect on the APB energy correlates with the variation of the ordering energy of the alloy according to the alloying element's position in the 3d row. The elements from the left side of the 3d row increase the APB energy of the Ni-based L1(2)-ordered alloys, while the elements from the right side slightly affect it except Ni. The way to predict the effect of an addition on the {111} APB energy in a multicomponent alloy is discussed.

  • 37.
    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.

  • 38.
    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.

  • 39.
    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)
  • 40.
    He, Shuang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Hunan University, China.
    Peng, Ping
    Gorbatov, Oleg I.
    Nosov Magnitogorsk State Technical University.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben Forschung GmbH, Austria.
    Effective interactions and atomic ordering in Ni-rich Ni-Re alloys2016In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 94, no 2, 024111Article in journal (Refereed)
    Abstract [en]

    Interatomic interactions and ordering in fcc Ni-rich Ni-Re alloys are studied by means of first-principles methods combined with statistical mechanics simulations based on the Ising Hamiltonian. First-principles calculations are employed to obtain effective chemical and strain-induced interactions, as well as ordering energies and enthalpies of formation of random and ordered Ni-Re alloys. Based on the nonmagnetic enthalpies of formation, we speculate that the type of ordering can be different in alloys with Re content less than 10 at.%. We demonstrate that effective chemical interactions in this system are quite sensitive to the alloy composition, atomic volume, and magnetic state. In statistical thermodynamic simulations, we have used renormalized interactions, which correctly reproduce ordering energies obtained in the direct total energy calculations. Monte Carlo simulations for Ni 0.91 Re 0.09   alloy show that there exists a strong ordering tendency of the (112 0)  type leading to precipitation of the D1 a   ordered structure at about 940 K. Our results for the atomic short-range order indicate, however, that the presently applied theory overestimates the strength of the ordering tendency compared to that observed in the experiment.

  • 41.
    He, Shuang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Peng, Ping
    Gorbatov, Oleg I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Nosov Magnitogorsk State Technical University, Russia.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben Forschung GmbH, Austria.
    Interactions and phase stability in Ni-rich Ni-W alloysManuscript (preprint) (Other academic)
    Abstract [en]

    Interatomic interactions and phase transformation in Ni-rich Ni-W alloys are investigated using rst-principlesmethods and statistical thermodynamics simulations. The formation enthalpies of fcc and bcc random as wellas some fcc-based ordered structures are determined in the ferromagnetic and nonmagnetic states. The effective interactions are calculated in supercell ab initio calculations and using screened generalized perturbation method(SGPM). We find the stable fcc-based ordered structures are D1a, DO22 and Pt2Mo phases and they can be observed in the Ni-25 at.% W, Ni-25 at.% W and Ni-33 at.% W alloys, respectively. The calculated atomic short-range order results are in reasonable agreement with experiments and other theoretical investigations.

  • 42.
    Hugosson, Håkan Wilhelm
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Eriksson, O.
    Jansson, U.
    Ruban, Andrei V.
    KTH, Superseded Departments, Materials Science and Engineering.
    Souvatis, P.
    Abrikosov, I. A.
    Surface energies and work functions of the transition metal carbides2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 557, no 03-jan, 243-254 p.Article in journal (Refereed)
    Abstract [en]

    We have performed an ab initio study of the surface energies, surface electronic structures and work functions for the (10 0) surface of the, existent and hypothetical, cubic 3d (Sc-Cu), 4d (Zr-Ag) and 5d (La-Au) transition metal carbides. The calculated surface energies have been compared to predictions using a so-called bond-cutting model and a model based on the so-called bonding energies. The absolute values and rough trends of the surface energies are fairly well predicted within the simple bond-cutting model, as compared to fully self-consistent calculations, while both trends and absolute values are well reproduced within the bonding energy model. The electronic structure (densities of states) of the transition metal carbides at the surface and in the bulk have been calculated. The trends are discussed in relation to the behavior of the surface energy and the work function across the series.

  • 43. Johannesson, G. H.
    et al.
    Bligaard, T.
    Ruban, Andrei V.
    Skriver, H. L.
    Jacobsen, K. W.
    Norskov, J. K.
    Combined electronic structure and evolutionary search approach to materials design2002In: Physical Review Letters, ISSN 0031-9007, Vol. 88, no 25Article in journal (Refereed)
    Abstract [en]

    We show that density functional theory calculations have reached an accuracy and speed making it possible to use them in conjunction with an evolutionary algorithm to search for materials with specific properties. The approach is illustrated by finding the most stable four component alloys out of the 192 016 possible fcc and bcc alloys that can be constructed out of 32 different metals. A number of well known and new super alloys are identified in this way.

  • 44.
    Johansson, Börje
    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.
    Abrikosov, I. A.
    Comment on "thermal signatures of the Kondo volume collapse in cerium"2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 18, 189601- p.Article in journal (Refereed)
    Abstract [en]

    A Comment on the Letter by M.J. Lipp et al., Phys. Rev. Lett.PRLTAO0031-9007 101, 165703 (2008)10.1103/PhysRevLett.101.165703

  • 45. Kabliman, E.
    et al.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Blaha, P.
    Schwarz, K.
    The atomic site occupancies in the Fe-Cr σ-phase2011In: 17th International Conference on Solid Compounds of Transition Elements, SCTE2010, 2011, 13-16 p.Conference paper (Refereed)
    Abstract [en]

    The atomic site distribution of the complex σ-phase structure (P42/mnm) has been studied using density functional theory (within the EMTO and WIEN2k codes) applying the cluster expansion method in a mean field approximation at finite temperatures. We found that at low temperatures Fe atoms predominantly occupy the icosahedrally coordinated (A,D) sites, Cr atoms prefer the (B,E) sites with the high coordination numbers, while the C site remains mixed. However, at higher temperature close to 1000 K all occupations become more and more mixed and reproduce well the available experimental data.

  • 46. Kabliman, Evgeniya
    et al.
    Blaha, Peter
    Schwarz, Karlheinz
    Peil, Oleg E.
    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.
    Configurational thermodynamics of the Fe-Cr sigma phase2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 18, 184206- p.Article in journal (Refereed)
    Abstract [en]

    Configurational thermodynamics of the Fe-Cr sigma phase is investigated on the basis of an Ising-type configurational Hamiltonian and a single-site mean-field model for the free energy. The parameters of the statistical models are obtained from efficient first-principles calculations using different computational techniques. We demonstrate that the effective pair and multisite interactions in the sigma phase are relatively small, which allows using a simplified model for distributing Fe and Cr atoms among sublattices. We also show that this system exhibits a nontrivial magnetic behavior at high temperatures, which affects the site occupation by Fe and Cr atoms. The structural variation (volume and c/a) that might be present due to neutron irradiation and thermal expansion can lead to an additional atomic redistribution.

  • 47. Kabliman, Evgeniya
    et al.
    Blaha, Peter
    Schwarz, Karlheinz
    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.
    Ab initio-based mean-field theory of the site occupation in the Fe-Cr sigma-phase2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 9, 092201- p.Article in journal (Refereed)
    Abstract [en]

    An efficient first-principles-based mean-field theory is applied to study the site occupations in the Fe-Cr sigma phase. It is based on the expansion of the total energy of a random alloy close to the equiatomic composition in the paramagnetic state in terms of the effective on-site interactions and takes into account longitudinal spin fluctuations at high temperatures. The calculated site occupation is in very good agreement with the existing experimental data.

  • 48. Kabliman, Evgeniya
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Blaha, Peter
    Peil, Oleg
    Schwarz, Karlheinz
    Ab Initio Study of Lattice Site Occupancies in Binary Sigma Phases Using a Single-Site Mean Field Model2012In: Applied Psychology Bulletin, ISSN 0006-6761, E-ISSN 2076-3417, Vol. 2, no 3, 654-668 p.Article in journal (Refereed)
    Abstract [en]

    The site occupation of binary Fe-Cr, Co-Cr, Re-W and Fe-V sigma phases is studied in the present work with a first-principles-based single-site mean field theory. We show that the alloy components in these systems exhibit similar site preferences except for the Re-W system, where the occupation of two sites is reversed in agreement with previously published works. In case of the FeV sigma phase, for which the size mismatch between the alloy components is large, we also include into our consideration the effect of local lattice relaxations. The obtained results are found in good agreement with the experimental data and previous theoretical studies.

  • 49. Khmelevska, T.
    et al.
    Khmelevskyi, S.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Mohn, P.
    Dependence of magnetism of VAu4 alloy on the state of chemical order: A first principles study2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 5Article in journal (Refereed)
    Abstract [en]

    The strong dependence of the magnetic properties of the alloy VAu4 upon the degree of chemical order has been a subject of intense experimental studies and controversial theoretical interpretations. In the framework of density functional theory using the coherent potential approximation embodied in the Korringa-Kohn-Rostoker method, we perform first principles calculations of VAu4 varying the degree of atomic chemical order from a disordered fcc alloy to the fully ordered MoNi4-type structure. In contrast to the conventional point of view, partially also based on earlier first principles studies of the ordered structure, our results suggest a localized character of the vanadium moments rather than being weakly itinerant. Moreover, we find that in the fully ordered alloy an antiferromagnetic state is more stable than the ferromagnetic. This finding leads to a significant revision of the earlier descriptions of magnetism in VAu4, which were based either on itinerant or local moment pictures. Investigating fcc Au-V alloys richer in vanadium, we also study the role of local environment effects on the stabilization of the magnetic moments at the V atoms and advocate a ferrimagnetic character of the experimentally observed state with a small spontaneous magnetization.

  • 50. Khmelevska, T.
    et al.
    Khmelevskyi, S.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Mohn, P.
    Magnetism and origin of non-monotonous concentration dependence of the bulk modulus in Fe-rich alloys with Si, Ge and Sn: a first-principles study2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 29, 6677-6689 p.Article in journal (Refereed)
    Abstract [en]

    Using the first-principles calculations based on the coherent potential approximation, we study the electronic structure, magnetic moments and the bulk modulus of FeX alloys with IVB group elements ( X = Si, Ge, Sn) in the Fe-rich concentration range (x = 0.0 - 0.25), which form a stability region of bcc-related phases. In agreement with experiment, our calculations reproduce well a peculiar non-monotonous behaviour of the bulk modulus in Fe - Si alloys with increasing Si concentration. Such a dependence is found for all bcc-related disordered and partially ordered Fe - Si phases A2, B2 and D0(3), which is in contrast with an earlier suggestion that the non-monotonous bulk modulus behaviour is related to partial ordering in Fe - Si. In addition, our results predict a similar behaviour in Fe - Ge and Fe - Sn alloys. It is shown that the observed behaviour of the bulk modulus is entirely related to the changes of the magnetic properties with chemical composition.

123 1 - 50 of 146
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