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  • 151. Jenkins, A. C.
    et al.
    Temmerman, W. M.
    Ahuja, R.
    Eriksson, O.
    Johansson, Börje
    Wills, J.
    The relationship between interlayer spacing and magnetic ordering in gadolinium2000Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, nr 50, s. 10441-10456Artikel i tidskrift (Refereegranskat)
  • 152. Jo, Minho
    et al.
    Koo, Yang Mo
    Lee, Byeong-Joo
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Theory for plasticity of face-centered cubic metals2014Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, nr 18, s. 6560-6565Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control.

  • 153. Johansson, Börje
    Structural and electronic relationships between the lanthanide and actinide elements2000Ingår i: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 128, nr 03-jan, s. 41-66Artikel i tidskrift (Refereegranskat)
  • 154. Johansson, Börje
    The many states of americium2000Ingår i: Physics world, ISSN 0953-8585, Vol. 13, nr 12, s. 26-27Artikel i tidskrift (Refereegranskat)
  • 155.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Thorium: The first 5f element in the actinide series2013Ingår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 245, s. 119-NUCL-Artikel i tidskrift (Övrigt vetenskapligt)
  • 156.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Klaesson, J.
    Distance decay for supply and demand potentials2016Ingår i: Letters in spatial and resource sciences, ISSN 1864-4031, E-ISSN 1864-404X, s. 1-22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper introduces a model framework which identifies the economic activity of each local economy (location) and observes the time distance between each pair of locations. Time distance for interaction inside local economies is taken as reference. Two models of location patterns are formulated on the basis of principles adhering to new economic geography (NEG). The first model describes how business service firms (classified into three levels of knowledge intensity) select locations with a favorable demand potential, depicting a location’s access to customer demand. The second model takes the location of business-service supply as given and describes how other firms select locations with a favorable supply potential, depicting the access to business-service supply. In order to calculate each location’s demand and supply potentials we need distance-decay parameters for interaction outside the local economy. When estimating the two models we develop an approach where the distance-decay (time sensitivity) parameters are determined endogenously as an integral part of estimating location choice parameters. The exercise can be appreciated as a test of NEG principles.

  • 157.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    Itinerant f-electron elements2009Ingår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, nr 22-24, s. 1793-1799Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To obtain a proper understanding of the 5f elements, the actinides, it is useful to compare their behavior with the 4f transition elements, the lanthanides. It is especially rewarding to capitalize on the remarkable similarity between the solid-state properties of compressed Ce and the actinide metals. The intensively studied alpha-gamma transition in Ce is considered to be a Mott transition, namely, the 4f electron changes its behavior from being localized to become delocalized (itinerant/metallic). This change also means that the 4f electron transforms from a non-bonding to a bonding configuration which, in turn, gives rise to a volume collapse. This collapse is isostructural in character, which contributes to the immense interest in this phase transition. An analogous and remarkable change in bonding (cohesive) properties is also found within the actinide series, where the sudden volume increase from Pu to Am (50%) can be viewed as a Mott transition within the 5f shell as a function of atomic number Z. The elements on the metallic side of the 5f Mott transition, i.e. the earlier actinides (Pa-Pu), show low symmetry structures at ambient conditions, while the heavier elements (from Am and beyond) adopt structures typical for the lighter trivalent lanthanide elements with localized 4f electrons. An important consequence of the localized and trivalent behavior in Am is a non-magnetic 5f(6) (J = L + S = 0) configuration for the f electrons. This led to the prediction of superconductivity in americium and subsequently to its experimental verification.

  • 158.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    The actinides - a beautiful ending of the Periodic Table2007Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 444, s. 202-206Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The 5f elements, actinides, show many properties which have direct correspondence to the 4f transition metals, the lanthanides. The remarkable similarity between the solid state properties of compressed Ce and the actinide metals is pointed out in the present paper. The alpha-gamma transition in Ce is considered as a Mott transition, namely, from delocalized to localized 4f states. An analogous behavior is also found for the actinide series, where the sudden volume increase from Pu to Am can be viewed upon as a Mott transition within the 5f shell as a function of the atomic number Z. On the itinerant side of the Mott transition, the earlier actinides (Pa-Pu) show low symmetry structures at ambient conditions; while across the border, the heavier elements (Am-Cf) present the dhcp structure, an atomic arrangement typical for the trivalent lanthanide elements with localized 4f magnetic moments. The reason for an isostructural Mott transition of the f electron in Ce, as opposed to the much more complicated cases in the actinides, is identified. The strange appearance of the delta-phase (fcc) in the phase diagram of Pu is another consequence of the border line behavior of the 5f electrons. The path leading from delta-Pu to alpha-Pu is identified.

  • 159.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Luo, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Li, Sa
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University.
    Cerium; Crystal Structure and Position in The Periodic Table2014Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, s. 6398-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of the cerium metal have intrigued physicists and chemists for many decades. In particular a lot of attention has been directed towards its high pressure behavior, where an isostructural volume collapse (gamma phase -> alpha phase) has been observed. Two main models of the electronic aspect of this transformation have been proposed; one where the 4f electron undergoes a change from being localized into an itinerant metallic state, and one where the focus is on the interaction between the 4f electron and the conduction electrons, often referred to as the Kondo volume collapse model. However, over the years it has been repeatedly questioned whether the cerium collapse really is isostructural. Most recently, detailed experiments have been able to remove this worrisome uncertainty. Therefore the isostructural aspect of the a-c transition has now to be seriously addressed in the theoretical modeling, something which has been very much neglected. A study of this fundamental characteristic of the cerium volume collapse is made in present paper and we show that the localized reversible arrow delocalized 4f electron picture provides an adequate description of this unique behavior. This agreement makes it possible to suggest that an appropriate crossroad position for cerium in The Periodic Table.

  • 160.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nilsson, D.
    Globalization and distribution of exports2012Ingår i: The Regional Economics of Knowledge and Talent: Local Advantage in a Global Context, Edward Elgar Publishing Ltd. , 2012, s. 300-319Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 161.
    Johansson, Börje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Comment on "thermal signatures of the Kondo volume collapse in cerium"2009Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, nr 18, s. 189601-Artikel i tidskrift (Refereegranskat)
    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

  • 162.
    Johansson, Börje
    et al.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Vitos, Levente
    Uppsala Universitet.
    Korzhavyi, Pavel A.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Chemical composition-elastic property maps of austenitic stainless steels2003Ingår i: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 5, nr 6, s. 931-936Artikel i tidskrift (Refereegranskat)
    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.

  • 163.
    Johansson, Börje Örje
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Isaev, E.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theoretical study of protactinium at high pressure2006Ingår i: Mater Res Soc Symp Proc, 2006, s. 255-269Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have studied the crystal structure of Pa metal under high pressure by means of first-principles calculations based on the density functional theory (DFT) using the generalized gradient approximation (GGA). The body centered tetragonal (bct) to orthorhombic (α-U) phase transition was calculated to take place at 29 GPa and with a volume change of 1.3%. The calculated c/a for the bet phase reaches the ideal c/a value (0.816) at around 50 GPa. A bulk modulus of 113 GPa was derived from a Murnaghan equation of state (EOS) fitting procedure. Our results are in general good agreement with recent experiment performed by Haire et al, [Phys. Rev. B 67, 134101 (2003)]. We have also calculated phonon spectra for fcc, bct and bcc Pa. The bcc spectrum gives imaginary frequencies showing the low temperature instability of this crystallographic phase for Pa.

  • 164.
    Jovanovic, Aleksandar
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Oberflachentechnol GmbH, CEST Kompetenzzentrum Elektrochem, Viktor Kaplan Str 2,Sect A, A-2700 Wiener Neustadt, Austria..
    Petkovic, Milena
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Humboldt Univ, Phys Dept, Zum Grossen Windkanal 6, D-12489 Berlin, Germany..
    Skorodumova, Natalia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Tuning the electronic and chemisorption properties of hexagonal MgO nanotubes by doping - Theoretical study2018Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 457, s. 1158-1166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Oxide materials offer a wide range of interesting physical and chemical properties. Even more versatile behavior of oxides is seen at the nanoscale, qualifying these materials for a number of applications. In this study we used DFT calculations to investigate the physical and chemical properties of small hexagonal MgO nanotubes of different length. We analyzed the effect of Li, B, C, N, and F doping on the properties of the nanotubes. We find that all dopants favor the edge positions when incorporated into the nanotubes. Doping results in the net magnetization whose value depends on the type of the impurity. Using the CO molecule as a probe, we studied the adsorption properties of pristine and doped MgO nanotubes. Our results show that the dopant sites are also the centers of significantly altered chemical reactivity. While pristine MgO nanotubes adsorb CO weakly, very strong adsorption at the dopant sites (B-, C-, and N-doped nanotubes) or neighboring edge atoms (F- and Li-doped nanotubes) is observed. Our results suggest that impurity engineering in oxide materials can be a promising strategy for the development of novel materials with possible use as selective adsorbents or catalysts.

  • 165. Jovanović, A.
    et al.
    Dobrota, A. S.
    Rafailović, L. D.
    Mentus, S. V.
    Pašti, Igor
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Belgrade, Faculty of Physical Chemistry, Serbia.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Humboldt University, Germany.
    Skorodumova, Natalia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Structural and electronic properties of V2O5 and their tuning by doping with 3d elements-modelling using the DFT+ U method and dispersion correction2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 20, s. 13934-13943Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New electrode materials for alkaline-ion batteries are a timely topic. Among many promising candidates, V2O5 is one of the most interesting cathode materials. While having very high theoretical capacity, in practice, its performance is hindered by its low stability and poor conductivity. As regards the theoretical descriptions of V2O5, common DFT-GGA calculations fail to reproduce both the electronic and crystal structures. While the band gap is underestimated, the interlayer spacing is overestimated as weak dispersion interactions are not properly described within GGA. Here we show that the combination of the DFT+U method and semi-empirical D2 correction can compensate for the drawbacks of the GGA when it comes to the modelling of V2O5. When compared to common PBE calculations, with a modest increase in the computational cost, PBE+U+D2 fully reproduced the experimental band gap of V2O5, while the errors in the lattice parameters are only a few percent. Using the proposed PBE+U+D2 methodology we studied the doping of V2O5 with 3d elements (from Sc to Zn). We show that both the structural and electronic parameters are affected by doping. Most importantly, a significant increase in conductivity is expected upon doping, which is of great importance for the application of V2O5 in metal-ion batteries.

  • 166. Kabliman, Evgeniya
    et al.
    Blaha, Peter
    Schwarz, Karlheinz
    Peil, Oleg E.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Configurational thermodynamics of the Fe-Cr sigma phase2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 18, s. 184206-Artikel i tidskrift (Refereegranskat)
    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.

  • 167. Kabliman, Evgeniya
    et al.
    Blaha, Peter
    Schwarz, Karlheinz
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio-based mean-field theory of the site occupation in the Fe-Cr sigma-phase2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 9, s. 092201-Artikel i tidskrift (Refereegranskat)
    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.

  • 168. Kadas, K.
    et al.
    Lindquist, M.
    Eriksson, O.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Magnetism-driven anomalous surface alloying between Cu and Cr2009Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cu-Cr contact materials are widely used as medium- and high-voltage vacuum interrupters. The microstructure of these materials is critical in their performance: the finer structure they have, the better are their physical properties. A solid solution of Cu and Cr could significantly increase the performance of such contact materials. However, Cu and Cr are practically immiscible in the bulk phase. Based on first principles density functional theory we show here that the solubility of Cr in Cu is dramatically increased on Cu surfaces already at room temperature and Cu-Cr alloys are formed on both the Cu(111) and Cu(100) surfaces. We demonstrate that the origin of this phenomenon is the unique magnetic properties of Cr atoms near surfaces.

  • 169. Kadas, K.
    et al.
    Nabi, Z.
    Kwon, S. K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Surface relaxation and surface stress of 4d transition metals2006Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 2, s. 395-402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the density functional theory formulated within the framework of the exact muffin-tin orbitals method, we present a systematic study of the top layer relaxation and surface stress of 4d transition metals. Our calculations predict layer contractions for most surfaces. We also find that the relaxations of the close packed surfaces decrease with increasing atomic number through the 4d series. We propose that the relaxation is mainly due to the reduction of the number of sp electrons in the surface layer relative to bulk. The surface stress is found to be very sensitive to the relaxation and, therefore, an accurate determination of the layer relaxation is necessary for obtaining reliable values for the surface stress. Comparing the top layer relaxations for the close packed surfaces, we see essential deviations between data derived in different ab initio calculations. At the same time, the overall trend for the present surface stress of 4d metals is in reasonable agreement with recent full-potential data.

  • 170. Kadas, K.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Temperature-dependent elastic properties of alpha-beryllium from first principles2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the temperature dependence of the structural parameters and the elastic properties of the hexagonal closed-packed phase of Be (alpha-Be). We find that the elastic constants follow a normal behavior with temperature: decrease with increasing temperature with a slightly increasing slope. Up to the melting point, the monocrystalline elastic constants decrease by an average of 16% and the polycrystalline elastic constants by 10%. These trends contradict the large temperature factor observed in high-temperature direct pulse ultrasonic experiments. At the same time, the low-temperature pulse echo measurements confirm the present theoretical findings. Our results call for further accurate experimental studies on the elastic properties of alpha-Be at high temperatures.

  • 171. Kadas, K.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Stability of body-centered cubic iron-magnesium alloys in the Earth's inner core2009Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, nr 37, s. 15560-15562Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The composition and the structure of the Earth's solid inner core are still unknown. Iron is accepted to be the main component of the core. Lately, the body-centered cubic (bcc) phase of iron was suggested to be present in the inner core, although its stability at core conditions is still in discussion. The higher density of pure iron compared with that of the Earth's core indicates the presence of light element(s) in this region, which could be responsible for the stability of the bcc phase. However, so far, none of the proposed composition models were in full agreement with seismic observations. The solubility of magnesium in hexagonal Fe has been found to increase significantly with increasing pressure, suggesting that Mg can also be an important element in the core. Here, we report a first-principles density functional study of bcc Fe-Mg alloys at core pressures and temperatures. We show that at core conditions, 5-10 atomic percent Mg stabilizes the bcc Fe both dynamically and thermodynamically. Our calculated density, elastic moduli, and sound velocities of bcc Fe-Mg alloys are consistent with those obtained from seismology, indicating that the bcc-structured Fe-Mg alloy is a possible model for the Earth's inner core.

  • 172. Kadas, K.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Structural stability of beta-beryllium2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using density-functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the stability of the body-centered-cubic phase of Be (beta-Be). The elastic constants and Debye temperature of beta-Be are calculated over a wide volume range and compared to those obtained for the low-temperature hexagonal phase (alpha-Be). A significant difference in the anisotropy of the bcc and hcp structures is found. In line with experiments, we predict that the hcp -> bcc phase transition occurs at 240 GPa at 0 K and 239 GPa at ambient temperature. We find that the cubic shear constant C '=(C-11-C-12)/2 rapidly decreases for volumes above similar to 1.05V(0), where V-0 is the zero temperature equilibrium volume for beta-Be. At 1.17V(0), the stability condition C-'> 0 is violated and the bcc phase becomes mechanically unstable. We demonstrate that at 0 K, the softening of beta-Be near its experimental volume of 1.063V(0) is related to an electronic topological transition due to the increased number of occupied s states near the Fermi level compared to that at V-0. This softening turns out to be important for the stability of the bcc phase before melting. The disclosed electronic topological transition is found to be present in other analogous hexagonal metals as well.

  • 173.
    Kadas, Krisztina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Eriksson, O.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermo-physical properties of body-centered cubic iron-magnesium alloys under extreme conditions2011Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 151, nr 3, s. 203-207Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C'). Magnesium alloying significantly increases C' of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in detail. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth's inner core as provided by seismic observations. (C) 2010 Elsevier Ltd. All rights reserved.

  • 174.
    Kadas, Krisztina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhang, Hualei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermo-physical properties of iron-magnesium alloys2011Ingår i: Magnesium Alloys - Design, Processing and Properties / [ed] Frank Czerwinski, InTech, 2011, s. 69-94Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 175. Karis, O.
    et al.
    Magnuson, M.
    Wiell, T.
    Weinelt, M.
    Wassdahl, N.
    Nilsson, A.
    Martensson, N.
    Holmstrom, E.
    Niklasson, A. M. N.
    Eriksson, O.
    Johansson, Börje
    Probing surface states of Cu/Ni thin films using x-ray absorption spectroscopy2001Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, nr 11, s. art. no.-113401Artikel i tidskrift (Refereegranskat)
  • 176. Karlsson, C.
    et al.
    Johansson, BörjeKTH, Skolan för industriell teknik och management (ITM).Kobayashi, K.Stough, R. R.
    Knowledge, innovation and space2014Samlingsverk (redaktörskap) (Övrigt vetenskapligt)
    Abstract [en]

    The contributions in this volume extend our understanding about the different ways distance impacts the knowledge conversion process. Knowledge itself is a raw input into the innovation process which can then transform it into an economically useful output such as prototypes, patents, licences and new companies. New knowledge is often tacit and thus tends to be highly localized, as indeed is the conversion process. Consequently, as the book demonstrates, space or distance matter significantly in the transformation of raw knowledge into beneficial knowledge.

  • 177. Karlsson, C.
    et al.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM).
    Kobayashi, K.
    Stough, R. R.
    Knowledge, innovation and space: Introduction2014Ingår i: Knowledge, Innovation and Space, Edward Elgar Publishing, 2014, s. 1-26Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 178. Karlsson, C.
    et al.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM).
    Kobayashi, K.
    Stough, R. R.
    Preface2014Ingår i: Knowledge, Innovation and Space: New Horizons in Regional Science series / [ed] Charlie Karlsson, Börje Johansson, Kiyoshi Kobayashi and Roger R. Stough, Edward Elgar Publishing, 2014, s. IX-XKapitel i bok, del av antologi (Refereegranskat)
  • 179. Karlsson, C.
    et al.
    Johansson, BörjeKTH, Skolan för industriell teknik och management (ITM).Stough, R. R.
    Agglomeration, clusters and entrepreneurship: Studies in regional economic development2014Samlingsverk (redaktörskap) (Övrigt vetenskapligt)
    Abstract [en]

    Regional economic development has experienced considerable dynamism over recent years. Perhaps the most notable cases were the rise of China and India to emergent country status by the turn of the millennium. With time now for hindsight, this book identifies some of the key forces behind these development successes, namely agglomeration, clusters and entrepreneurship.

  • 180. Karlsson, C.
    et al.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM).
    Stough, R. R.
    Preface2014Ingår i: Agglomeration, Clusters and Entrepreneurship: Studies in Regional Economic Development / [ed] Charlie Karlsson, Börje Johansson and Roger R. Stough, Edward Elgar Publishing, 2014, s. x-xiKapitel i bok, del av antologi (Refereegranskat)
  • 181. Khmelevskyi, S.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kakehashi, Y.
    Mohn, P.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio investigation of the Invar anomaly in ordered fcc Fe-Pt alloys2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The magnetovolume anomaly in ordered fcc Fe-Pt Invar alloys is studied by ab inito Korringa-Kohn-Rostoker atomic-sphere approximation technique in the framework of density-functional theory. The paramagnetic state above the magnetic ordering transition temperature is treated using the disordered local moment (DLM) approach. We show that the DLM approach is able to describe and explain the Invar anomaly in ordered Fe-rich Fe-Pt alloys similarly to our previous work for the disordered modification. In particular, our calculations predict the weakening of the Invar anomaly in chemically ordered compositions as compared to the disordered case as well as a decreasing magnetovolume anomaly with increasing Pt concentrations for both ordered and disordered cases in full agreement with experimental observations. The detailed study of the Fe3Pt compound with varying chemical long-range order has revealed a continuously decreasing spontaneous volume magnetostriction with increasing degree of order. This can be understood from the corresponding band structure of random and ordered alloys.

  • 182. Koci, L.
    et al.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Study of the high-pressure helium phase diagram using molecular dynamics2007Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rich occurrence of helium and hydrogen in space makes their properties highly interesting. By means of molecular dynamics ( MD), we have examined two interatomic potentials for He-4. Both potentials are demonstrated to reproduce high-pressure solid and liquid equation of state (EOS) data. The EOS, solid - solid transitions and melting at high pressures ( P) were studied using a two-phase method. The Buckingham potential shows a good agreement with theoretical and experimental EOS, but does not reproduce experimental melting data. The Aziz potential shows a perfect match with theoretical melting data. We conclude that there is a stable body-centred-cubic (bcc) phase for He-4 at temperatures ( T) above 340 K and pressures above 22 GPa for the Buckingham potential, whereas no bcc phase is found for the Aziz potential in the applied PT range.

  • 183. Kokko, K.
    et al.
    Ropo, M.
    Punkkinen, M. P. J.
    Laukkanen, P.
    Alatalo, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Surface core-level shift of Pd at the AgcPd1-c(111) surface: Nonlinear subsurface effects2007Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 23, s. 5419-5423Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surface core-level binding-energy shift (SCLS) of Pd at the AgcPd1-c(111) surface is calculated as a function of bulk concentration of the alloy. The equilibrium volume and the surface concentration profile used in the calculations refer to the 0 K case. The SCLSs are evaluated within the Z + 1 approximation. The results are analysed using the mixing enthalpy of the alloy and the bulk and surface chemical potentials. A relation of the SCLS to the bulk concentration is considered. This relation is shown to be mediated by the surface concentration profile which induces the observed nonlinear behaviour. The results are interpreted using a simple model for the alloy electronic structure.

  • 184. Kollar, J.
    et al.
    Vitos, Levente
    Johansson, Börje
    Skriver, H. L.
    Metal surfaces: Surface, step and kink formation energies2000Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 217, nr 1, s. 405-418Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We review the surface, step, and kink energies in monoatomic metallic systems. A systematic comparison is given between the theoretical results based on density functional theory and available experimental data. Our calculated values are used to predict the equilibrium shapes of small metal particles, monoatomic surface islands, and the instability of different surface geometries.

  • 185.
    Korzhavyi, Pavel A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Thermodynamic properties of copper compounds with oxygen and hydrogen from first principles2010Rapport (Refereegranskat)
    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.

  • 186.
    Korzhavyi, Pavel A.
    et al.
    KTH, Tidigare Institutioner, Materialvetenskap.
    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, Tidigare Institutioner, Materialvetenskap.
    Ab Initio Study of Phase Equilibria in TiCx2002Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, nr 1, s. 015505-1-01505-4Artikel i tidskrift (Refereegranskat)
    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.

  • 187.
    Korzhavyi, Pavel A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Odqvist, J.
    Nilsson, J.-O.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Electronic structure and effective chemical and magnetic exchange interactions in bcc Fe-Cr alloys2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 5, s. 054202-Artikel, forskningsöversikt (Refereegranskat)
    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.

  • 188.
    Korzhavyi, Pavel A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-principles calculations as a new tool in steel research2008Ingår i: 6th European Stainless Steel Conference, Science and Market Helsinki, Finland, June 10-13, 2008: Proceedings / [ed] P. Karjalainen and S. Hertzman, Jernkontoret , 2008, s. 279-284Konferensbidrag (Refereegranskat)
    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.

  • 189.
    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 NiAl2000Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, nr 9, s. 6003-6018Artikel i tidskrift (Refereegranskat)
    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.

  • 190.
    Korzhavyi, Pavel A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Soroka, Inna
    Uppsala Universitet.
    Boman, Mats
    Uppsala Universitet.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Thermodynamics of stable and metastable Cu-O-H compounds2011Konferensbidrag (Refereegranskat)
    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.

  • 191.
    Korzhavyi, Pavel A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Soroka, Inna L.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Isaev, Eyvaz I.
    Lilja, Christina
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Exploring monovalent copper compounds with oxygen and hydrogen2012Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, nr 3, s. 686-689Artikel i tidskrift (Refereegranskat)
    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.

  • 192.
    Korzhavyi, Pavel A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sundman, Bo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Selleby, Malin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Atomic, electronic, and magnetic structure of iron-based sigma-phases2005Ingår i: Integrative and Interdisciplinary Aspects of Intermetallics / [ed] MIlls, MJ; Inui, H; Clemens, H; Fu, CL, WARRENDALE: MATERIALS RESEARCH SOCIETY , 2005, Vol. 842, s. 517-522Konferensbidrag (Refereegranskat)
    Abstract [en]

    A combination of ab initio total energy calculations with Calphad approach is applied to model the site occupancy and thermodynamic properties of the Fe-Cr, Co-Cr, Fe-V, and Fe-Mo binary sigma-phases as a function of composition and temperature. For each binary sigma-phase the parameters of the model are the ab initio calculated total energies of so-called end-member compounds, which represent all the 2(5)=32 variants of complete occupancy of each of the five crystallographically inequivalent sites by one or the other alloy component, The paramagnetic state of the sigma-phases has been taken into account within the disordered local moment approach. The Fe and Co atoms are found to retain high spin moments when they occupy high-coordination-number sites in the structure. Using our model we were able to reproduce the experimentally observed site occupancy in the FeCr sigma-phase. The calculated site occupancies in the Co-Cr, Fe-V, and Fe-Mo sigma-phases are also presented and discussed.

  • 193.
    Korzhavyi, Pavel A.
    et al.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Vitos, Levente
    KTH, Tidigare Institutioner, Materialvetenskap.
    Andersson, David A.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Oxidation of plutonium dioxide2004Ingår i: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 3, nr 4, s. 225-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The physics and chemistry of the actinide elements form the scientific basis for rational handling of nuclear materials(1-3). In recent experiments(4), most unexpectedly, plutonium dioxide has been found to react with water to form higher oxides up to PuO2.27, whereas PuO2 had always been thought to be the highest stable oxide of plutonium(2,3). We perform a theoretical analysis of this complicated situation on the basis of total energies calculated within density functional theory(5,6) combined with well-established thermodynamic data. The reactions of PuO2 with either O-2 or H2O to form PuO2+delta are calculated to be endothermic: that is, in order to occur they require a supply of energy. However, our calculations show that PuO2+delta can be formed, as an intermediate product, by reactions with the products of radiolysis of water, such as H2O2.

  • 194.
    Korzhavyi, Pavel A.
    et al.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Vitos, Levente
    KTH, Tidigare Institutioner, Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Thermodynamic properties of Pu-O-H compounds and alloys from density functional theory2004Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII / [ed] Oversby, VM; Werme, LO, WARRENDALE: Materials Research Society, 2004, Vol. 807, s. 107-112Konferensbidrag (Refereegranskat)
    Abstract [en]

    A theoretical approach has been developed that allows one to obtain thermodynamic properties of plutonium-based alloys and compounds from first-principles electronic structure calculations based on density functional theory. The approach is applied to study the defect structure in non-stoichiometric PuO2+/-delta.

  • 195. Kouba, R.
    et al.
    Taga, A.
    Ambrosch-Draxl, C.
    Nordstrom, L.
    Johansson, Börje
    Phonons and electron-phonon interaction by linear-response theory within the LAPW method2001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6418, nr 18Artikel i tidskrift (Refereegranskat)
  • 196. Krisch, Michael
    et al.
    Farber, D. L.
    Xu, R.
    Antonangeli, Daniele
    Aracne, C. M.
    Beraud, Alexandre
    Chiang, Tai-Chang
    Zarestky, J.
    Kim, Duck Young
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Isaev, Eyvaz I.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Phonons of the anomalous element cerium2011Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 23, s. 9342-9345Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many physical and chemical properties of the light rare-earths and actinides are governed by the active role of f electrons, and despite intensive efforts the details of the mechanisms of phase stability and transformation are not fully understood. A prominent example which has attracted a lot of interest, both experimentally and theoretically over the years is the isostructural gamma-alpha transition in cerium. We have determined by inelastic X-ray scattering, the complete phonon dispersion scheme of elemental cerium across the gamma -> alpha transition, and compared it with theoretical results using ab initio lattice dynamics. Several phonon branches show strong changes in the dispersion shape, indicating large modifications in the interactions between phonons and conduction electrons. This is reflected as well by the lattice Gruneisen parameters, particularly around the X point. We derive a vibrational entropy change Delta S-vib(gamma-alpha) approximate to (0.33 +/- 0.03)k(B), illustrating the importance of the lattice contribution to the transition. Additionally, we compare first principles calculations with the experiments to shed light on the mechanism underlying the isostructural volume collapse in cerium under pressure.

  • 197. Kuronen, A.
    et al.
    Granroth, S.
    Heinonen, M. H.
    Perala, R. E.
    Kilpi, T.
    Laukkanen, P.
    Lang, J.
    Dahl, J.
    Punkkinen, M. P. J.
    Kokko, K.
    Ropo, M.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Segregation, precipitation, and alpha-alpha ' phase separation in Fe-Cr alloys2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 21, artikel-id 214113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Iron-chromium alloys, the base components of various stainless steel grades, have numerous technologically and scientifically interesting properties. However, these features are not yet sufficiently understood to allow their full exploitation in technological applications. In this work, we investigate segregation, precipitation, and phase separation in Fe-Cr systems analyzing the physical mechanisms behind the observed phenomena. To get a comprehensive picture of Fe-Cr alloys as a function of composition, temperature, and time the present investigation combines Monte Carlo simulations using semiempirical interatomic potential, first-principles total energy calculations, and experimental spectroscopy. In order to obtain a general picture of the relation of the atomic interactions and properties of Fe-Cr alloys in bulk, surface, and interface regions several complementary methods have to be used. Using the exact muffin-tin orbitals method with the coherent potential approximation (CPA-EMTO) the effective chemical potential as a function of Cr content (0-15 at. % Cr) is calculated for a surface, second atomic layer, and bulk. At similar to 10 at. % Cr in the alloy the reversal of the driving force of a Cr atom to occupy either bulk or surface sites is obtained. The Cr-containing surfaces are expected when the Cr content exceeds similar to 10 at. %. The second atomic layer forms about a 0.3 eV barrier for the migration of Cr atoms between the bulk and surface atomic layer. To get information on Fe-Cr in larger scales we use semiempirical methods. However, for Cr concentration regions less than 10 at. %, the ab initio (CPA-EMTO) result of the important role of the second atomic layer to the surface is not reproducible from the large-scale Monte Carlo molecular dynamics (MCMD) simulation. On the other hand, for the nominal concentration of Cr larger than 10 at. % the MCMD simulations show the precipitation of Cr into isolated pockets in bulk Fe-Cr and the existence of the upper limit of the solubility of Cr into Fe layers in Fe/Cr layer systems. For high Cr concentration alloys the performed spectroscopic measurements support the MCMD simulations. Hard x-ray photoelectron spectroscopy and Auger electron spectroscopy investigations were carried out to explore Cr segregation and precipitation in the Fe/Cr double layer and Fe0.95Cr0.05 and Fe0.85Cr0.15 alloys. Initial oxidation of Fe-Cr was investigated experimentally at 10(-8) Torr pressure of the spectrometers showing intense Cr2O3 signal. Cr segregation and the formation of Cr-rich precipitates were traced by analyzing the experimental atomic concentrations and chemical shifts with respect to annealing time, Cr content, and kinetic energy of the exited electron.

  • 198. Kuzmin, M.
    et al.
    Punkkinen, M. J. P.
    Laukkanen, P.
    Lang, J. J. K.
    Dahl, J.
    Tuominen, V.
    Tuominen, M.
    Perala, R. E.
    Balasubramanian, T.
    Adell, J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, K.
    Vayrynen, I. J.
    Surface core-level shifts on Ge(111)c(2 x 8): Experiment and theory2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 24, s. 245319-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Combining high-resolution photoelectron spectroscopy and density functional theory (DFT) calculations, 3d photoemission line shape and surface core-level shifts have been reinvestigated on the Ge(111)c(2 x 8) surface. It is found that 3d spectra include, in addition to the bulk and three surface-shifted components reported in literature, a component that was not identified in earlier measurements with a lower resolution. The detailed interpretation of these spectra and their line shape is made on the basis of DFT calculations. It is shown that the lowest binding energy component is due to the rest atoms. The higher binding energy emission is caused by the adatoms and the third-layer atoms that are below the adatoms. Finally, the two other surface components originate from the first- and second-layer atoms. The screening effects in the Ge(111)c(2 x 8) are discussed.

  • 199. Kuzmin, M.
    et al.
    Punkkinen, M. P. J.
    Laukkanen, P.
    Perala, R. E.
    Tuominen, V.
    Lang, J. J. K.
    Ahola-Tuomi, M.
    Dahl, J.
    Balasubramanian, T.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vayrynen, I. J.
    Atomic structure of Yb/Si(100)(2X6): Interrelation between the silicon dimer arrangement and Si 2p photoemission line shape2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 11, s. 113302-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Combining photoelectron spectroscopy and density-functional theory calculations, we have studied the atomic geometry of Yb/Si(100)(2 X 6) reconstruction and the mechanisms responsible for its stabilization as well as the influence of this reconstruction on Si 2p core-level photoemission. The analysis of measured and calculated surface core-level shifts supports the recently proposed model of the Yb/Si(100)(2 X 6). It involves, in agreement with valence-band measurements, unbuckled (symmetrical) silicon dimers, leading to unusually narrowed Si 2p line shape as compared to those of related systems. The origin of the symmetrical dimers in the (2 X 6) structure is discussed in the context of previous results in literature.

  • 200. Kwon, S. K.
    et al.
    Nabi, Z.
    Kadas, K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Surface energy and stress release by layer relaxation2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surface energy (gamma) and surface stress (tau) for semi-infinite close-packed surfaces of 4d transition metals have been calculated using ab initio total-energy methods. The moderate agreement between the present and former theoretical data for tau indicates the high level of numerical difficulty associated with such calculations. For the most close-packed surfaces, the present unrelaxed tau values follow the typical trend characteristic for the cohesive energy in nonmagnetic transition-metal series, whereas the relaxed tau values group around similar to 1 mJ/m(2), obtained for Y, Zr, and Ag, and similar to 3 mJ/m(2), calculated for Nb, Mo, Tc, Ru, Rh, and Pd. We have found that the average surface energy reduction upon layer relaxation is around 4%. At the same time, a large part of the surface stress is released during the surface relaxation process. To explain the observed behaviors, we have established a simple relationship, which connects the variations of gamma and tau to the layer relaxation. This relation reveals the principal factors determining the difference between the surface energy and stress release rates at 4d transition-metal surfaces.

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