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Johansson, Börje
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Publications (10 of 263) Show all publications
Al-Zoubi, N., Schönecker, S., Johansson, B. & Vitos, L. (2017). Assessing the Exact Muffin-Tin Orbitals method for the Bain path of metals. Philosophical Magazine, 97(15), 1243-1264.
Open this publication in new window or tab >>Assessing the Exact Muffin-Tin Orbitals method for the Bain path of metals
2017 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 97, no 15, p. 1243-1264Article in journal (Refereed) Published
Abstract [en]

We scrutinise the muffin-tin approximation and the screening within the framework of the Exact Muffin-Tin Orbitals method in the case of cubic and tetragonal crystal symmetries. Systematic total energy calculations are carried out for the Bain path including the body-centred cubic and face-centred cubic structures for a set of simple and transition metals. The present converged results in terms of potential sphere radius (S) and hard sphere radius (b) are in good agreement with previous theoretical calculations. We demonstrate that for all structures considered here, potential sphere radii around and slightly larger than the average Wigner-Seitz radius (w) yield accurate total energy results whereas S values smaller than w give large errors. It is shown that for converged total energies hard spheres with radii b = 0.7-0.8w should be used for an efficient screening within real space clusters consisting typically of 70-90 lattice sites. The less efficient convergence of the total energy in the case of small hard spheres is ascribed to the delocalisation of the screened spherical waves, which leads to inaccurate interstitial overlap matrix. The above conclusions are not significantly affected by the volume of the system.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2017
Keyword
The Bain path, Transition metals, The Exact Muffin-Tin Orbital (EMTO) method
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-322885 (URN)10.1080/14786435.2017.1293862 (DOI)000399958500005 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2017-05-31 Created: 2017-05-31 Last updated: 2017-05-31Bibliographically approved
Li, X., Schönecker, S., Zhao, J., Vitos, L. & Johansson, B. (2017). Elastic anharmonicity of bcc Fe and Fe-based random alloys from first-principles calculations. Physical Review B, 95(2), Article ID 024203.
Open this publication in new window or tab >>Elastic anharmonicity of bcc Fe and Fe-based random alloys from first-principles calculations
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 2, article id 024203Article in journal (Refereed) Published
Abstract [en]

We systematically investigate elastic anharmonic behavior in ferromagnetic body-centered cubic (bcc) Fe and Fe1-xMx (M = Al, V, Cr, Co, or Ni) random alloys by means of density-functional simulations. To benchmark computational accuracy, three ab initio codes are used to obtain the complete set of second-and third-order elastic constants (TOECs) for bcc Fe. The TOECs of Fe1-xMx alloys are studied employing the first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. It is found that the alloying effects on C-111, C-112, and C-123, which are governed by normal strains only, are more pronounced than those on C-144, C-166, and C-456, which involve shear strains. Remarkably, the magnitudes of all TOECs but C-123 decrease upon alloying with Al, V, Cr, Co, or Ni. Using the computed TOECs, we study compositional effects on the pressure derivatives of the effective elastic constants (dB(ij)/dP), bulk (dK/dP), and shear moduli (dG/dP) and derive longitudinal acoustic nonlinearity parameters (beta). Our predictions show that the pressure derivatives of K and G decrease with x for all solute elements and reveal a strong correlation between the compositional trends on dK/dP and dG/dP arising from the fact that alloying predominantly altersdB(11)/dP. The sensitivity of dB(11)/dP to composition is attributed to intrinsic alloying effects as opposed to lattice parameter changes accompanying solute addition. For Fe and the considered Fe-based alloys, beta along high-symmetry directions orders as beta[111] > beta[100] > beta[110], and alloying increases the directional anisotropy of beta but reduces its magnitude.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-315812 (URN)10.1103/PhysRevB.95.024203 (DOI)000391852800001 ()
Funder
Carl Tryggers foundation Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2017-02-22 Created: 2017-02-22 Last updated: 2017-11-29Bibliographically approved
Dobrota, A. S., Pasti, I. A., Mentus, S. V., Johansson, B. & Skorodumova, N. V. (2017). Functionalized graphene for sodium battery applications: the DFT insights. Electrochimica Acta, 250, 185-195.
Open this publication in new window or tab >>Functionalized graphene for sodium battery applications: the DFT insights
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2017 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 250, p. 185-195Article in journal (Refereed) Published
Abstract [en]

Considering the increasing interest in the use of graphene-based materials for energy conversion and storage applications, we have performed a DFT study of Na interaction with doped graphene, both in non-oxidized and oxidized forms. Oxidation seems to play the crucial role when it comes to the interaction of doped graphene materials with sodium. The dopants act as attractors of OH groups, making the material prone to oxidation, and therefore altering its affinity towards Na. In some cases, this can result in hydroxide or water formation - an irreversible change lethal for battery performance. Our results suggest that one should carefully control the oxidation level of doped graphene-based materials if they are to be used as sodium battery electrode materials as the optimal oxidation level depends on the dopant type.

Keyword
Graphene, Doping, Oxidation, Sodium storage, Energy conversion, Reactivity
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-336302 (URN)10.1016/j.electacta.2017.07.186 (DOI)000410679300023 ()
Available from: 2018-01-23 Created: 2018-01-23 Last updated: 2018-01-23Bibliographically approved
Fu, J., Li, X., Johansson, B. & Zhao, J. (2017). Improved Finnis-Sinclair potential for vanadium-rich V-Ti-Cr ternary alloys. Journal of Alloys and Compounds, 705, 369-375.
Open this publication in new window or tab >>Improved Finnis-Sinclair potential for vanadium-rich V-Ti-Cr ternary alloys
2017 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 705, p. 369-375Article in journal (Refereed) Published
Abstract [en]

We have developed an improved Finnis-Sinclair (IFS) potential for vanadium-rich V-Ti-Cr random alloys with body-centred cubic structure. An extra exponential term is added to the original FS potential to enhance the repulsive interaction. The IFS potential is fitted to experimental crystal structure, cohesive energy and elastic constants of pure metals (V, Ti and Cr) and theoretical data of binary alloys (V15Ti, V15Cr and Ti8Cr8). The good agreement of the predicted formation energies of mono-vacancy and selfinterstitial of octahedral interstitial site, tetrahedral interstitial site, < 111>-dumbbell, < 110>-dumbbell, and < 100>-dumbbell with available experimental and theoretical data confirms the validity of our IFS potential in pure V. Furthermore, the agreement of elastic properties and defect properties of typical alloy (V-4-Ti-4-Cr) with experimental or DFT data also support the applicability of the IFS potential in Vrich ternary V-Ti-Cr alloys. Finally, this work also provides a reference to develop empirical potentials for other ternary alloys.

Keyword
Finnis-Sinclair potential, V-Ti-Cr alloy, Defect properties, Mechanical properties
National Category
Metallurgy and Metallic Materials Materials Engineering
Identifiers
urn:nbn:se:uu:diva-321166 (URN)10.1016/j.jallcom.2017.02.103 (DOI)000397994700049 ()
Funder
Carl Tryggers foundation , CTS15:241
Available from: 2017-05-15 Created: 2017-05-15 Last updated: 2017-05-15Bibliographically approved
Li, C.-M., Johansson, B. & Vitos, L. (2017). Physical mechanism of delta-delta '-epsilon phase stability in plutonium. Scientific Reports, 7, Article ID 5632.
Open this publication in new window or tab >>Physical mechanism of delta-delta '-epsilon phase stability in plutonium
2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 5632Article in journal (Refereed) Published
Abstract [en]

Based on first-principle calculations, we have systematically explored the nature of the elastic stability and the delta-delta'-epsilon phase transitions in pure Pu at high temperature. It is found that, both the electronphonon coupling and the spin fluctuation effects tend to decrease the tetragonal elastic constant (C') of delta-Pu, accounting for its anomalous softening at high temperature. The lattice thermal expansion together with the electron-phonon coupling can stiffen C' of epsilon-Pu, promoting its mechanical stability at high temperature. The delta-epsilon transition is calculated to take place around 750-800 K, and is dominated by the phonon vibration. The delta' intermediate phase is realized around 750 K mainly because of the thermal spin fluctuation.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-331235 (URN)10.1038/s41598-017-06009-1 (DOI)000405677200017 ()28717177 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2017-10-16Bibliographically approved
Li, X., Schonecker, S., Li, R., Li, X., Wang, Y., Zhao, J., . . . Vitos, L. (2016). Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys: effects of transmutation of W. Journal of Physics: Condensed Matter, 28(29), Article ID 295501.
Open this publication in new window or tab >>Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys: effects of transmutation of W
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2016 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 29, article id 295501Article in journal (Refereed) Published
Abstract [en]

To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-yRexOsy (0 <= x, y <= 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young's modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C-11, the other elastic parameters including C-12, C-44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W-Re-Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch-Nabarro model for solid-solution hardening predicts larger strengthening effects in W1-yOsy than in W1-xRex. A strong correlation between C' and the fcc-bcc structural energy difference for W1-x-yRexOsy is revealed demonstrating that canonical band structure dictates the alloying effect on C'. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.

Keyword
disordered W-Re-Os alloys, elastic properties, ductility, solid-solution hardening
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-299024 (URN)10.1088/0953-8984/28/29/295501 (DOI)000377504100007 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2016-07-14 Created: 2016-07-13 Last updated: 2017-11-28Bibliographically approved
Li, G., Eriksson, O., Johansson, B. & Vitos, L. (2016). Ab initio investigation of competing antiferromagnetic structures in low Si-content FeMn(PSi) alloy. Journal of Physics: Condensed Matter, 28(21), Article ID 216002.
Open this publication in new window or tab >>Ab initio investigation of competing antiferromagnetic structures in low Si-content FeMn(PSi) alloy
2016 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 21, article id 216002Article in journal (Refereed) Published
Abstract [en]

The antiferromagnetic structures of a low Si-content FeMn(PSi) alloy were investigated by first principles calculations. One possible antiferromagnetic structure in supercell along the c-axis was revealed in FeMnP0.75Si0.25 alloy. It was found that atomic disorder occupation between Fe atom on 3f and Mn atoms on 3g sites is responsible for the formation of antiferromagnetic structures. Furthermore the magnetic competition and the coupling between possible AFM supercells along the c and a-axis can promote a non-collinear antiferromagnetic structure. These theoretical investigations help to deeply understand the magnetic order in FeMn(PSi) alloys and benefit to explore the potential magnetocaloric materials in Fe2P-type alloys.

Keyword
antiferromagnetic structures, FeMn(PSi) alloy, magnetocaloric materials
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-302219 (URN)10.1088/0953-8984/28/21/216002 (DOI)000376409400009 ()27143642 (PubMedID)
External cooperation:
Funder
Swedish Research CouncilEU, European Research CouncilCarl Tryggers foundation StandUpKnut and Alice Wallenberg FoundationeSSENCE - An eScience Collaboration
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2017-11-21Bibliographically approved
Li, X., Schönecker, S., Zhao, J., Johansson, B. & Vitos, L. (2016). Alloying effect on the ideal tensile strength of ferromagnetic and paramagnetic bcc iron. Journal of Alloys and Compounds, 676, 565-574.
Open this publication in new window or tab >>Alloying effect on the ideal tensile strength of ferromagnetic and paramagnetic bcc iron
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2016 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 676, p. 565-574Article in journal (Refereed) Published
Abstract [en]

Using ab initio alloy theory formulated within the exact muffin-tin orbitals theory in combination with the coherent potential approximation, we investigate the ideal tensile strength (ITS) in the [001] direction of bcc ferro-/ferrimagnetic (FFM) and paramagnetic (PM) Fe1-xMx (M = Al, V, Cr, Mn, Co, or Ni) random alloys. The ITS of ferromagnetic (FM) Fe is calculated to be 12.6 GPa, in agreement with available data, while the PM phase turns out to posses a significantly lower value of 0.7 GPa. Alloyed to the FM matrix, we predict that V, Cr, and Co increase the ITS of Fe, while Al and Ni decrease it. Manganese yields a weak non-monotonic alloying behavior. In comparison to FM Fe, the alloying effect of Al and Co to PM Fe is reversed and the relative magnitude of the ITS can be altered more strongly for any of the solutes. All considered binaries are intrinsically brittle and fail by cleavage of the (001) planes under uniaxial tensile loading in both magnetic phases. We show that the previously established ITS model based on structural energy differences proves successful in the PM Fe-alloys but is of limited use in the case of the FFM Fe-based alloys. The different performance is attributed to the specific interplay between magnetism and volume change in response to uniaxial tension. We establish a strong correlation between the compositional effect on the ITS and the one on the shear elastic constant C' for the PM Fe-alloys and briefly discuss the relation between hardenability and the ITS.

Keyword
Fe-based alloys, Ideal tensile strength, ab initio, Structural energy difference
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-297245 (URN)10.1016/j.jallcom.2016.03.218 (DOI)000374328100074 ()
Funder
Swedish Research CouncilEU, European Research Council
Available from: 2016-06-29 Created: 2016-06-22 Last updated: 2017-11-28Bibliographically approved
Li, C.-M., Yang, R., Johansson, B. & Vitos, L. (2016). Anomalous thermodynamic properties and phase stability of delta-Pu1-xMx (M = Ga and Al) alloys from first-principles calculations. Physical Review B, 94(21), Article ID 214108.
Open this publication in new window or tab >>Anomalous thermodynamic properties and phase stability of delta-Pu1-xMx (M = Ga and Al) alloys from first-principles calculations
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 21, article id 214108Article in journal (Refereed) Published
Abstract [en]

The composition-dependent crystal structure, volume, elastic constants, and electronic structure of delta-Pu1-xMx (M = Ga and Al, 0 <= x <= 0.1) alloys are systematically studied by using first-principles EMTO-CPA calculations. It is shown that the fcc and L1(2) structures co-exist in the alloys with x <= 0.04 whereas for x > 0.04, the L1(2) structure is more and more preferable and around x = 0.1, it tends to be stabilized alone. The evaluated V similar to x of the L1(2) structure, being negative deviation from Vegard's law, turns out to be in good agreement with the experimental result. For x <= 0.04, the estimated E, G, nu, and Theta of both the fcc and L1(2) structures are in line with the measured data, whereas when x > 0.04, only those of the L1(2) structure are close to the experimental results. The electronic hybridization between Pu and M atoms is dominated by Pu for the s, d, and f states but M for the p state. The strong interactions between Pu and M atoms in the same site of the L1(2) structure should be responsible for its relative stability in the alloys withx > 0.04. The electron-phonon coupling further decreases the phase stability of delta-Pu1-xMx with increasing x.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-313530 (URN)10.1103/PhysRevB.94.214108 (DOI)000390248900002 ()
Available from: 2017-02-02 Created: 2017-01-20 Last updated: 2017-11-29Bibliographically approved
Li, W., Lu, S., Hu, Q.-M., Johansson, B., Kwon, S. K., Grehk, M., . . . Vitos, L. (2016). Generalized stacking fault energy of gamma-Fe. Philosophical Magazine, 96(6), 524-541.
Open this publication in new window or tab >>Generalized stacking fault energy of gamma-Fe
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2016 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 96, no 6, p. 524-541Article in journal (Refereed) Published
Abstract [en]

We investigate the generalized stacking fault energy ( [GRAPHICS] -surface) of paramagnetic [GRAPHICS] -Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along the [GRAPHICS] -surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking fault formation regime ( [GRAPHICS] K) towards maximum twinning ( [GRAPHICS] K) and finally to a dominating full-slip regime ( [GRAPHICS] K). Our predictions are discussed in connection with the available experimental observations.

Keyword
-Fe, plasticity, stacking fault energy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-283788 (URN)10.1080/14786435.2016.1140912 (DOI)000372097300001 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research EU, European Research Council
Available from: 2016-04-14 Created: 2016-04-14 Last updated: 2017-11-30Bibliographically approved
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