Ändra sökning
Avgränsa sökresultatet
45678910 301 - 350 av 458
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 301. Osorio-Guillen, J. M.
    et al.
    Holm, B.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    A theoretical study of olivine LiMPO4 cathodes2004Ingår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 167, nr 3-4, s. 221-227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on a density functional theory (DFT) calculation of the properties of LiMPO4, where M is either Fe, Mn or Co. The mixing between Fe and Mn in these structures is also examined. We have derived three relevant battery properties, namely average voltage, energy density and specific energy, as well as the lattice constants and ionic coordinates for each case examined. Our calculated values for these properties are in good agreement with recent experimental values, when available. Further insight is gained from the electronic density of states of the phases, through which conclusions about the physical properties of the various phases are made.

  • 302. Osorio-Guillen, J. M.
    et al.
    Simak, S. I.
    Wang, Y.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Ahuja, R.
    Bonding and elastic properties of superconducting MgB22002Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 123, nr 07-jun, s. 257-262Artikel i tidskrift (Refereegranskat)
  • 303. Palmquist, J. P.
    et al.
    Li, S.
    Persson, P. O. A.
    Emmerlich, J.
    Wilhelmsson, O.
    Hogberg, H.
    Katsnelson, M. I.
    Johansson, Börje
    Ahuja, R.
    Eriksson, O.
    Hultman, L.
    Jansson, U.
    M(n+1)AX(n) phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 16Artikel i tidskrift (Refereegranskat)
  • 304.
    Pasti, Igor A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. 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..
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Tunable reactivity of supported single metal atoms by impurity engineering of the MgO(001) support2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 9, s. 6337-6346Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Development of novel materials may often require a rational use of high price components, like noble metals, in combination with the possibility to tune their properties in a desirable way. Here we present a theoretical DFT study of Au and Pd single atoms supported by doped MgO(001). By introducing B, C and N impurities into the MgO(001) surface, the interaction between the surface and the supported metal adatoms can be adjusted. Impurity atoms act as strong binding sites for Au and Pd adatoms and can help to produce highly dispersed metal particles. The reactivity of metal atoms supported by doped MgO(001), as probed by CO, is altered compared to their counterparts on pristine MgO(001). We find that Pd atoms on doped MgO(001) are less reactive than on perfect MgO(001). In contrast, Au adatoms bind CO much more strongly when placed on doped MgO(001). In the case of Au on N-doped MgO(001) we find that charge redistribution between the metal atom and impurity takes place even when not in direct contact, which enhances the interaction of Au with CO. The presented results suggest possible ways for optimizing the reactivity of oxide supported metal catalysts through impurity engineering.

  • 305.
    Pasti, Igor A.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Jovanovic, Aleksandar
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;CEST Kompetenzzentrum Elektrochem Oberfiachentecn, Viktor Kaplan Str 2,Sect A, A-2700 Wiener Neustadt, Austria..
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Dept Phys & Astron, POB 516, S-75120 Uppsala, Sweden..
    Skorodumova, Natalia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Dept Phys & Astron, POB 516, S-75120 Uppsala, Sweden..
    Atomic adsorption on pristine graphene along the Periodic Table of Elements - From PBE to non-local functionals2018Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 436, s. 433-440Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The understanding of atomic adsorption on graphene is of high importance for many advanced technologies. Here we present a complete database of the atomic adsorption energies for the elements of the Periodic Table up to the atomic number 86 (excluding lanthanides) on pristine graphene. The energies have been calculated using the projector augmented wave (PAW) method with PBE, long-range dispersion interaction corrected PBE (PBE+D2, PBE+D3) as well as non-local vdW-DF2 approach. The inclusion of dispersion interactions leads to an exothermic adsorption for all the investigated elements. Dispersion interactions are found to be of particular importance for the adsorption of low atomic weight earth alkaline metals, coinage and s-metals (11th and 12th groups), high atomic weight p-elements and noble gases. We discuss the observed adsorption trends along the groups and rows of the Periodic Table as well some computational aspects of modelling atomic adsorption on graphene.

  • 306. Pasti, Igor A.
    et al.
    Jovanovic, Aleksandar
    Dobrota, Ana S.
    Mentus, Slavko V.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden.
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden.
    Atomic adsorption on graphene with a single vacancy: systematic DFT study through the periodic table of elements2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 2, s. 858-865Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vacancies in graphene present sites of altered chemical reactivity and open possibilities to tune graphene properties by defect engineering. The understanding of chemical reactivity of such defects is essential for successful implementation of carbon materials in advanced technologies. We report the results of a systematic DFT study of atomic adsorption on graphene with a single vacancy for the elements of rows 1-6 of the periodic table of elements (PTE), excluding lanthanides. The calculations have been performed using the PBE, long-range dispersion interaction-corrected PBE (PBE+D2 and PBE+D3) and non-local vdW-DF2 functionals. We find that most elements strongly bind to the vacancy, except for the elements of groups 11 and 12, and noble gases, for which the contribution of dispersion interaction to bonding is most significant. The strength of the interaction with the vacancy correlates with the cohesive energy of the elements in their stable phases: the higher the cohesive energy is, the stronger bonding to the vacancy can be expected. As most atoms can be trapped at the SV site we have calculated the potentials of dissolution and found that in most cases the metals adsorbed at the vacancy are more "noble" than they are in their corresponding stable phases.

  • 307. Peil, O. E.
    et al.
    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 study of atomic ordering and spin-glass transition in dilute CuMn alloys2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An archetypical spin-glass metallic alloy, Cu0.83Mn0.17, is studied by means of an ab initio based approach. First-principles calculations are employed to obtain effective chemical, strain-induced, and magnetic exchange interactions, as well as static atomic displacements, and the interactions are subsequently used in thermodynamic simulations. It is shown that the calculated atomic and magnetic short-range order accurately reproduces the results of neutron-scattering experiments. In particular, it is confirmed that the alloy exhibits a tendency toward ordering and the corresponding ordered phase is revealed. The magnetic structure is represented by spin-spiral clusters accompanied by weaker ferromagnetic short-range correlations. The spin-glass transition temperature obtained in Monte Carlo simulations by a finite-size scaling technique, 57 K, is in reasonable agreement with experimental data, 78 K.

  • 308. Peil, O. E.
    et al.
    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.
    Detailed ab initio calculations of the structure and magnetic state of a metallic spin glass2008Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present for the first time a long-sought atomic and magnetic structure of one of the most well-known and studied spin-glass systems: the Cu83Mn17 alloy, which is the prototype for a large class of metallic spin-glass systems. The structure has been determined from simulations based on atomic and magnetic interactions obtained from first-principles calculations. Being in perfect agreement with recent neutron scattering experiments, our results reveal the atomic and magnetic structure that exhibits a specific short-range order (SRO) and is believed to be responsible for a complicated magnetic cluster dynamics leading to the spin-glass behaviour in this alloy. The ordered phase underlying the atomic SRO is shown to have a Cu3Mn-type structure with 16 atoms per unit cell. The magnetic SRO is associated with incommensurate spin-spiral correlations.

  • 309. Peil, O. E.
    et al.
    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.
    Self-consistent supercell approach to alloys with local environment effects2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 16, s. 165140-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an efficient and accurate method for calculating electronic structure and related properties of random alloys with a proper treatment of local environment effects. The method is a generalization of the locally self-consistent Green's-function technique for the exact muffin-tin orbital method. An alloy system in the calculations is represented by a supercell with a certain set of atomic-distribution correlation functions. The Green's function for each atom in the supercell is obtained by embedding the cluster of neighboring atoms lying within a local interaction zone (LIZ) into an effective medium and solving the cluster Dyson equation exactly. The key ingredients of the method are locality, which makes it linearly scaling with the number of atoms in the supercell, and coherent-potential self-consistency of the effective medium, which results in a fast convergence of the electronic structure with respect to the LIZ size. To test the performance and accuracy of the method, we apply it to two systems: Fe-rich bcc-FeCr random alloy with and without a short-range order, and a Cr impurity on the Fe surface. Both cases demonstrate the importance of taking into account the local environment effects for correct description of magnetic and bulk properties.

  • 310. Peil, Oleg E.
    et al.
    Johansson, Börje
    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.
    Ab initio investigation of magnetic ordering and spin-glass transition in Cu-rich Cu-Mn systems2007Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 310, nr 2, s. 1561-1563Artikel i tidskrift (Refereegranskat)
  • 311. Persson, Clas
    et al.
    Ahuja, R.
    da Silva, A. F.
    Johansson, Börje
    First-principle calculations of optical properties of wurtzite AlN and GaN2001Ingår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 231, nr 3, s. 407-414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The imaginary part of the dielectric function of wurtzite AIN and GaN has been calculated in the long wavelength limit, using two different first-principle electronic structure methods. The first method is a full-potential linearized augmented plane wave method and the second is a full-potential linear muffin-tin orbital method. From the Kramers-Kronig dispersion relations the real part of the dielectric function has been obtained, taking into account a quasi-particle band-gap correction according to Bechstedt and Del Sole. Absorption due to optical phonons is treated as a delta function in the imaginary part of the dielectric function. Both the longitudinal as well as the transverse components of the dielectric function are presented, showing that the anisotropy is small in these materials. Although we use different correlation potentials in the two methods, the results are similar, We compare our calculated dielectric functions with spectroscopic ellipsometry and reflectance spectra measurements.

  • 312. Persson, Clas
    et al.
    Ahuja, R.
    da Silva, A. F.
    Johansson, Börje
    First-principle calculations of the dielectric function of zinc-blende and wurtzite InN2001Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, nr 40, s. 8945-8950Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The imaginary part of the dielectric function of zinc-blende and wurtzite InN has been calculated using a full-potential linearized augmented plane wave method. We show that the exchange potential of Engel and Vosko gives an insulating ground state for both structures. The real part of the dielectric function has been obtained from the Kramers-Kronig dispersion relations, assuming a quasiparticle band-gap correction according to Bechstedt and Del Sole. We have found that it is necessary to have a good account of the band gap in order to derive the low-frequency optical properties. We present the longitudinal as wen as the transverse components in wurtzite InN, showing that the anisotropy is small.

  • 313.
    Persson, Clas
    et al.
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Full band calculation of doping-induced band-gap narrowing in p-type GaAs2001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6403, nr 3, s. art. no.-033201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have calculated the energy shift of the fundamental band gap as a function of dopant concentration in p-type GaAs, using a perturbation theory based on the zero-temperature Green's function formalism within the random-phase approximation. The electronic structure of the intrinsic crystal was obtained from a relativistic, full-potential band-structure calculation, with the exchange potential of Engel and Vosko [Phys. Rev. B 47, 13164 (1993)]. We have found that this potential gives accurate band curvatures at the band edges. The nonparabolicity of the uppermost valence bands has a reducing effect on the energy shifts of both the conduction and valence bands for high acceptor, concentrations. The resulting narrowing of the band gap is in good agreement with photoluminescence measurements. Thus, it is crucial to take into account the full band structure to calculate the band-gap narrowing accurately for high acceptor concentrations.

  • 314. Persson, Clas
    et al.
    da Silva, A. F.
    Ahuja, R.
    Johansson, Börje
    Effective electronic masses in wurtzite and zinc-blende GaN and AlN2001Ingår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 231, nr 3, s. 397-406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effective electron and hole masses are fundamental quantities of semiconductors, used in numerous analyses of experiments and theoretical investigations. We present calculations of the band structure near the band edges in intrinsic GaN and AIN, both for the wurtzite and the zinc-blende polytypes. We have utilized a full-potential linearized augmented plane wave method within the density functional theory and with two different exchange-correlation potentials. The lattice parameters have been determined by a minimization of the total energy, whereupon the crystal-field splitting, the spin-orbit splitting, and the effective electron and hole masses have been calculated. The calculated effective masses are in good agreement with available experimental values. We show the importance of performing a fully relativistic calculation. For instance, the hole mass in cubic AIN is a very large and negative quantity if the spin-orbit coupling is excluded, whereas the fully relativistic calculation gives a relatively small and positive value.

  • 315. Persson, Clas
    et al.
    da Silva, A. F.
    Johansson, Börje
    Metal-nonmetal transition in p-type SiC polytypes2001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6320, nr 20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The critical concentration for the metal-nonmetal transition has been calculated fur the polytypes 3C, 4H, and 6H of SiC, duped with Al, Ga, B, and Sc. Three different computational methods have been utilized: the first is Mott's original model, the second is an extended Mott-Hubbard model, and the third is based on the total energy of the metallic and nonmetallic phases. All three methods show similar results. For comparison, calculations fur p-type Ge and Si materials have also been performed.

  • 316. Persson, Clas
    et al.
    Sernelius, B. E.
    da Silva, A. F.
    Ahuja, R.
    Johansson, Börje
    Effective electron and hole masses in intrinsic and heavily n-type doped GaN and AlN2001Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, nr 40, s. 8915-8922Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated the electronic structure near the band edges in intrinsic and heavily n-type doped GaN and AlN. Both the wurtzite and the zincblende polytypes have been considered. The electronic structures of the intrinsic materials were obtained from a full-potential linearized augmented plane wave calculation. We show the importance of performing a fully relativistic calculation. For instance, the hole mass in cubic AIN is a very large and negative quantity if spin-orbit coupling is excluded, whereas the fully relativistic calculation gives a relatively small and positive value. The electron-phonon coupling was taken into account according to the Frohlich Hamiltonian for large polarons, resulting in effective polaron masses. The effects on the effective electron masses due to doping were investigated by using a Green's function formalism within the random phase approximation and with a local-field correction according to Hubbard.

  • 317. Persson, Clas
    et al.
    Sernelius, B. E.
    da Silva, A. F.
    Araujo, C. M.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Optical and reduced band gap in n- and p-type GaN and AlN2002Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, nr 6, s. 3207-3216Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a full band calculation of the doping-induced energy shifts of the conduction-band minimum and the valence-band maximum for n- and p-type GaN and AlN. Both wurtzite and zinc-blende structures have been considered. The resulting optical and reduced band-gap energies are presented as functions of the ionized impurity concentration in the heavily doped regime. The computational method is based on a zero-temperature Green's function formalism within the random phase approximation and with the local-field correction of Hubbard. The calculation goes beyond the spherical approximation of the energy bands by using energy dispersions and overlap integrals from a first-principle, full-potential band-structure calculation. Inclusion of the spin-orbit interaction is crucial for describing the uppermost valence bands properly, and we show that the nonparabolicity of the valence bands influences the energy shifts strongly, especially the shift of the optical band gap. With the full band structure, we can explain the results of photoluminescence measurements by Yoshikawa [J. Appl. Phys. 86, 4400 (1999)].

  • 318. Peters, L.
    et al.
    Di Marco, I.
    Litsarev, M. S.
    Delin, A.
    Katsnelson, M. I.
    Kirilyuk, A.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden.
    Sanyal, B.
    Eriksson, O.
    Valence and spectral properties of rare-earth clusters2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 3, artikel-id 035143Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rare earths are known to have intriguing changes of the valence, depending on the chemical surrounding or geometry. Here, we aim at predicting the transition of valence when passing from the atomic divalent limit to the bulk trivalent limit. This transition is analyzed by addressing clusters of various size for selected rare-earth elements, i.e., Sm, Tb, and Tm, via a theoretical treatment that combines density functional theory with atomic multiplet theory. Our results show that Tm clusters change from pure divalent to pure trivalent at a size of six atoms, while Tb clusters are already divalent for two atoms and stay so until eight atoms and the bulk limit. Instead, Sm clusters are respectively purely divalent up to eight atoms. For larger Sm clusters, a transition to a trivalent configuration is expected and likely accompanied by a regime of mixed valence. The valence of all rare-earth clusters, as a function of size, is predicted from the interpolation of our calculated results. These predictions are argued to be best investigated by spectroscopic measurements. To ease experimental analysis, we provide theoretical spectra, based on dynamical mean-field theory in the Hubbard I approximation.

  • 319. Pitkänen, H.
    et al.
    Alatalo, M.
    Puisto, A.
    Ropo, Matti
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, K.
    Punkkinen, M. P. J.
    Olsson, P.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hertzman, Staffan N.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio study of the phase stability in paramagnetic duplex steel alloys2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Duplex stainless steels have many superior properties compared to conventional steels, this being mainly due to their microstructure containing approximately equal amount of ferrite and austenite phases formed by iron, chromium (or Cr equivalent), and nickel (or Ni equivalent). Using computational methods based on first-principles theories, the phase stability of paramagnetic Fe1-c-nCrcNin alloys (0.12 <= c <= 0.32 and 0.04 <= n <= 0.32) at high temperatures (greater than or similar to 1000 K) is addressed. It is shown that the stabilization of the ferrite-austenite two-phase field in duplex steels is a result of complex interplay of several competing phenomena. Taking into account only the formation energies yields a complete phase separation, strongly overestimating the two-phase region. The formation energies are calculated to be lower for the austenite than for the ferrite, meaning that the configurational entropy has a more significant impact on the stability field of the austenitic phase. The magnetic and vibrational free energies have opposite effects on the phase stability. Namely, the magnetic entropy favors the ferrite phase, whereas the vibrational free energy stabilizes the austenite phase. Combining the formation energies with the magnetic, vibrational, and configurational free energies, a region of coexistence between the two phases is obtained, in line with former thermodynamic assessments as well as with experimental observations.

  • 320. Pitkänen, H.
    et al.
    Alatalo, M.
    Puisto, A.
    Ropo, Matti
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Kokko, K.
    Punkkinen, M. P. J.
    Olsson, Pär
    Department of Materials and Mechanics of Components, France.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hertzman, Staffan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ab initio study of the phase stability in paramagnetic duplex steel alloys (Erratum)2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the paper the Gibbs energy components are first discussed in the case of the Fe0.84−nCr0.16Nin quasi-binary system (Sec.III A) and then for the Fe1−c−nCrcNin ternary alloys (Sec. III B). Since the above constant-Cr cross-section is not along the tielines1 of the ternary Fe-Cr-Ni phase diagram, our results from Sec. III A should not be connected at all to the ternary diagramreported, e.g., in Ref. 2. In particular, the last two sentences from the first paragraph and the second sentence from the lastparagraph (Sec. III.) should be ignored. The discussion from Sec. III A remains strictly valid only for a hypothetical binarysystem.

    Since the conclusions from the paper are based on the results presented in Sec. III B, they are not affected by the aboveerroneous interpretation of the results obtained for the quasi-binary system.

    The authors are grateful to Bo Sundman and John Ågren for pointing out this flaw in the paper.

  • 321. Ponomareva, A.
    et al.
    Isaev, E. I.
    Pourovskii, L.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Abrikosov, I. A.
    Ab initio investigations of surface magnetism in V-Mo2004Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 272-276, s. 1198-1200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic properties of the (0 0 1) surface of pure vanadium and disordered binary Mo-V alloys have been investigated from the first-principles by means of the LMTO-GF-CPA technique, the fixed spin moment method, and the direct exchange Monte-Carlo statistical mechanics simulations. The binary alloys, as well as pure constituent metals, are nonmagnetic in the bulk. However, we have shown that the (1 0 0) surface of uniformly random and segregated Mo-V alloys is magnetic. The magnetism of the V monolayer on the Mo(0 0 1) surface has also been studied. In particular, the surface relaxation effect has resulted in a reduction of the magnetic moments for V atoms, but the surface magnetism is still present in the system. Including of semi-core states as valence ones does not alter this conclusion.

  • 322. Ponomareva, A. V.
    et al.
    Pourovskii, L. V.
    Isaev, E. I.
    Vekilov, Y. K.
    Abrikosov, I. A.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Surface magnetism of the PdV binary alloys2002Ingår i: Physics of low-Dimensional structures, ISSN 0204-3467, Vol. 02-jan, s. 337-349Artikel i tidskrift (Refereegranskat)
  • 323. Ponomareva, A. V.
    et al.
    Pourovskii, L. V.
    Isaev, E. I.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Abrikosov, I. A.
    Magnetization of the unsegregated and segregated (100) surface of MoV binary alloys2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 6Artikel i tidskrift (Refereegranskat)
  • 324. Ponomareva, A. V.
    et al.
    Pourovskii, L. V.
    Isaev, E. I.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Abrikosov, I. A.
    Surface magnetism of vanadium-based binary alloys: first principles investigations2003Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 258, s. 128-130Artikel i tidskrift (Refereegranskat)
  • 325. Pourovskii, L. V.
    et al.
    Ruban, Andrei V.
    Abrikosov, I. A.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Bulk ordering and surface segregation in Ni50Pt502001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6403, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interatomic interactions obtained from the effective screened generalized-perturbation method have been applied in Monte Carlo simulations to derive the bulk and surface-alloy configurations for Ni50Pt50 The calculated order-disorder transition temperature and short-range order parameters in the bulk compare well with experimental data. The surface-alloy compositions for the (111) and (110) facets above the ordering transition temperature are also found to be in a good agreement with experiments. It is demonstrated that the segregation profile at the (110) surface of NiPt is mainly caused by the unusually strong segregation of Pt into the second layer and the interlayer ordering due to large chemical nearest-neighbor interactions.

  • 326. Pourovskii, L. V.
    et al.
    Ruban, Andrei V.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Abrikosov, I. A.
    Antisite-defect-induced surface segregation in ordered NiPt alloy2003Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 90, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By means of first principles simulations we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L1(0) ordered alloy have a great impact on the atomic configuration of the (111) surface. We predict that at T=600 K the (111) surface of the Ni51Pt49 and Ni50Pt50 alloys corresponds to the (111) truncation of the bulk L1(0) ordered structure. However, the (111) surface of the nickel deficient Ni49Pt51 alloy is strongly enriched by Pt and should exhibit the pattern of the 2x2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys and is a manifestation of the so-called off-stoichiometric effect.

  • 327. Pourovskii, L. V.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ebert, H.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Fully relativistic spin-polarized exact muffin-tin-orbital method2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, nr 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The exact muffin-tin-orbital (EMTO) method is generalized for fully relativistic (FR) spin-polarized calculations. In the present implementation we solve self-consistently the four-component Dirac equation by using the Green's function formalism. Substitutional disorder is treated within the coherent potential approximation. To obtain accurate total energies we use the full-charge density technique. We apply the FR-EMTO Green's function method to calculate the ground-state properties of delta-Pu. We also calculate spin and orbital magnetic moments in random bcc, fcc, and hcp Fe-Co alloys, as well as in the B2 ordered and partially ordered phase.

  • 328. Poyurovskii, L. V.
    et al.
    Ruban, Andrei V.
    Abrikosov, I. A.
    Vekilov, Y. K.
    Johansson, Börje
    Application of the Monte Carlo method to the problem of surface segregation simulation2001Ingår i: JETP Letters: Journal of Experimental And Theoretical Physics Letters, ISSN 0021-3640, E-ISSN 1090-6487, Vol. 73, nr 8, s. 415-419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A generalization of the Monte Carlo method to the case of grand canonical ensemble allowing the elimination of the problem of determination of the chemical potential of alloy components was proposed. The method is particularly convenient for the calculations of surface segregations because it excludes time-consuming calculation of the temperature-dependent bulk chemical potential mu (T). The new method was used for calculating segregations at the (100), (110), and (111) surfaces of the Ni50Pd50 alloy using the Ising model with ab initio effective interatomic interaction potentials.

  • 329. Punkkinen, M. P. J.
    et al.
    Kokko, K.
    Ropo, M.
    Vayrynen, I. J.
    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.
    Magnetism of (FeCo)Si alloys: Extreme sensitivity on crystal structure2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theoretical results for (FeCo)Si substitutional random alloys, obtained within the framework of the exact muffin-tin orbitals method in combination with the coherent potential approximation, are presented. For concentration range 0.1 < x < 0.9, the magnetic structure of Fe1-xCoxSi is found to be almost degenerate, which is reflected in extreme sensitivity of the local magnetic moments on the internal structure parameters and lattice constant. Results are analyzed and discussed using Stoner, covalent magnetism, and rigid band models. In Fe-rich and in Co-rich alloys, the composition dependence of the magnetic moments can be understood in terms of a simple model. It is shown that disorder has a significant effect on magnetism in (FeCo)Si alloys.

  • 330. Punkkinen, M. P. J.
    et al.
    Kokko, K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Laukkanen, P.
    Airiskallio, E.
    Ropo, M.
    Ahola-Tuomi, M.
    Kuzmin, M.
    Vayrynen, I. J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Calculation of surface core-level shifts within complete screening: Problems with pseudohydrogenated slabs2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By considering GaAs(110) and Si(100)(2x1) surfaces, it is shown that the use of the pseudohydrogen atoms to saturate the dangling bonds at one side of the slab modeling a free surface can lead to distorted surface core-level shifts within the complete screening picture. The effect is linked to the polarization of the slab and to the change in the bulklike electronic structure close to pseudohydrogenated part of the slab. It is demonstrated that these problems can be avoided if the pseudohydrogenated slab is large enough and the bulk reference layer is properly chosen. One easy way to control these errors is to monitor the planar-averaged potential energy curve of the slab.

  • 331. Punkkinen, M. P. J.
    et al.
    Laukkanen, P.
    Kokko, K.
    Ropo, M.
    Ahola-Tuomi, M.
    Vayrynen, I. J.
    Komsa, H. P.
    Rantala, T. T.
    Pessa, M.
    Kuzmin, 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 shifts of GaAs(100)(2x4) from first principles2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles calculations show that measured surface core-level shifts (SCLSs) of the GaAs(100)(2x4) surfaces can be described within the initial state effects. The calculated As 3d and Ga 3d SCLSs for the beta 2 and alpha 2 reconstructions of the GaAs(100)(2x4) surfaces are in reasonable agreement with recent measurements. In particular, the results confirm that both the lower and the higher binding energy SCLSs, relative to the bulk emission in the As 3d photoelectron spectra, are intrinsic properties of the GaAs(100)(2x4) surfaces. The most positive and most negative As shifts are attributed to the third layer As atoms, which differs from the previous intuitive suggestions. In general, calculations show that significant SCLSs arise from deep layers, and that there are more than two SCLSs. Our previously measured As 3d spectra are fitted afresh using the calculated SCLSs. The intensity ratios of the SCLSs, obtained from the fits, show that as the heating temperature of the GaAs(100)(2x4) surface is increased gradually, the area of the alpha 2 reconstruction increases on the surface, but the beta 2 phase remains within the whole temperature range, in agreement with previous experimental findings. Our results show that the combination of the experimental and theoretical results is a prerequisite for the accurate analysis of the SCLSs of the complex reconstructed surfaces.

  • 332. Punkkinen, M. P. J.
    et al.
    Laukkanen, P.
    Komsa, H. P.
    Ahola-Tuomi, M.
    Rasanen, N.
    Kokko, K.
    Kuzmin, M.
    Adell, J.
    Sadowski, J.
    Perala, R. E.
    Ropo, M.
    Rantala, T. T.
    Vayrynen, I. J.
    Pessa, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Mirbt, S.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Bismuth-stabilized (2x1) and (2x4) reconstructions on GaAs(100) surfaces: Combined first-principles, photoemission, and scanning tunneling microscopy study2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bismuth adsorbate-stabilized (2x1) and (2x4) reconstructions of the GaAs(100) surfaces have been studied by first-principles calculations, valence-band and core-level photoelectron spectroscopies, and scanning tunneling microscopy. It is demonstrated that large Bi atom size leads to the formation of the pseudogap at the Fermi energy and to the lower energy of an adsorbate-derived surface band, which contributes to the stabilization of the exceptional Bi/GaAs(100)(2x1) reconstruction. It is proposed that the Bi/GaAs(100)(2x4) reconstructions include asymmetric mixed Bi-As dimers, in addition to the Bi-Bi dimers. Based on the calculations, we solve the atomic origins of the surface core-level shifts (SCLSs) of the Bi 5d photoemission spectra from the Bi/GaAs(100)(2x4) surfaces. This allows for resolving the puzzle related to the identification of two SCLS components often found in the measurements of the Bi 5d and Sb 4d core-level emissions of the Bi/III-V and Sb/III-V(100)(2x4) surfaces. Finally, the reason for the absence of the common (2x4)-beta 2 structure and additional support for the stability of the (2x1) structure on the Bi/III-V(100) surfaces are discussed in terms of Bi atom size and subsurface stress.

  • 333.
    Punkkinen, Marko P. J.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kuzmin, M.
    Laukkanen, P.
    Perala, R. E.
    Ahola-Tuomi, M.
    Lang, J.
    Ropo, M.
    Pessa, M.
    Vayrynen, I. J.
    Kokko, K.
    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.
    Stability and structure of rare-earth metal and Ba-induced reconstructions on a Si(100) surface2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, nr 23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied, by means of ab initio calculations, the energetics and the atomic and electronic structures of various reconstructions induced by rare-earth metals (RE=Eu, Nd, Sm, and Yb) and Ba on Si(100) in the coverage range up to 0.5 monolayer. It is shown that Si dimer buckling is an important structural element for such systems, leading frequently to oblique surface lattice symmetries. The strong metal atom-silicon binding favors the increased amount of metal atoms per unit surface area, i.e., the (2x3) reconstruction with two metal atoms per unit cell is found to be energetically unstable with respect to the (2x1) reconstruction with three metal atoms per the same surface area [Eu/Si(100) and Yb/Si(100)]. The influence of the atomic size and the valence of the adsorbates is also investigated. In particular, it is found that an increase in atomic size stimulates the metal-metal repulsion, stabilizing the (2x3) configuration [Ba/Si(100)]. In the case of trivalent metals, the stabilization of the (2x3) is mediated by the loss of semiconducting state in the competing phases [Sm/Si(100) and Nd/Si(100)]. Our results demonstrate the importance of many factors, which account for the abundance of RE/Si(100) reconstructions. Finally, prominent atomic models are proposed for (2x3) and (2x6) reconstructions, and the character of the wavy "(1x2)" reconstruction is discussed. The simulated scanning tunneling microscopy images for the proposed (2x6) reconstruction are in a particularly good agreement with the complex experimental images.

  • 334.
    Punkkinen, Marko P. J.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Laukkanen, P.
    Ahola-Tuomi, M.
    Pakarinen, J.
    Kuzmin, M.
    Tukiainen, A.
    Perala, R. E.
    Lang, J.
    Ropo, M.
    Kokko, K.
    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.
    Pessa, M.
    Vayrynen, I. J.
    Core-level shifts of InP(100)(2 x 4) surface: Theory and experiment2009Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 16, s. 2664-2668Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface core-level shifts (SCLSs) of the (2 x 4)-reconstructed InP(100) surface with the established mixed In-P dimer structure have been investigated by first-principles calculations and photoelectron spectroscopy. Theoretical values were calculated using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy functional. The obtained theoretical values are quite similar within both approximations. The found differences originate in the tiny structural differences. It is concluded that the expansion or contraction of the crystal lattice has smaller effect on the SCLSs than the geometrical details of the reconstruction, which suggests that the Madelung potential has the dominant effect on the SCLSs. The results support the presence of a P 2p peak at higher binding energy (BE) compared to bulk peak, as proposed with recent measurements [P. Laukkamen, J. Pakarinen, M. Ahola-Tuomi, M. Kuzmin, R. E. Perala, I. J. Vayrynen, A. Tukiainen, V. Rimpilainen, M. Pessa, M. Adell, J. Sadowski, Surf. Sci. 600 (2006) 3022], and reveal several hitherto not reported SCLSs. The calculated SCLSs reproduce the measured spectra within reasonable accuracy. Furthermore, the atomic origins of the InP(100)(2 x 4) SCLSs are solved. In particular, it is shown that the lowest SCLS of P 2p, of the InP(100)(2 x 4) arises from the topmost In-P dimers.

  • 335.
    Punkkinen, Marko Patrick John
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, K.
    Levämäki, H.
    Ropo, M.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg, Lorand
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhang, Hualei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg-Czirjak, Erna Krisztina
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    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.
    Adhesion of the iron-chromium oxide interface from first-principles theory2013Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 49, s. 495501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.

  • 336.
    Punkkinen, Marko Patrick John
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Kwon, S. K.
    Kollar, 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.
    Compressive Surface Stress in Magnetic Transition Metals2011Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, nr 5, s. 057202-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Because of the increased electron density within the surface layer, metal surfaces are generally expected to have tensile surface stress. Here, using first-principles density functional calculations, we demonstrate that in magnetic 3d metals surface magnetism can alter this commonly accepted picture. We find that the thermodynamically stable surfaces of chromium and manganese possess compressive surface stress. The revealed negative surface stress is shown to be ascribed to the enhanced magnetic moments within the surface layer relative to the bulk values.

  • 337.
    Punkkinen, Marko Patrick John
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Laukkanen, P.
    Lang, J.
    Kuzmin, M.
    Tuominen, M.
    Tuominen, V.
    Dahl, J.
    Pessa, M.
    Guina, M.
    Kokko, K.
    Sadowski, J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vayrynen, I. J.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Oxidized In-containing III-V(100) surfaces: Formation of crystalline oxide films and semiconductor-oxide interfaces2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 19, s. 195329-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previously found oxidized III-V semiconductor surfaces have been generally structurally disordered and useless for applications. We disclose a family of well-ordered oxidized InAs, InGaAs, InP, and InSb surfaces found by experiments. The found epitaxial oxide-III-V interface is insulating and free of defects related to the harmful Fermi-level pinning, which opens up new possibilities to develop long-sought III-V metal-oxide-semiconductor transistors. Calculations reveal that the early stages in the oxidation process include only O-III bonds due to the geometry of the III-V(100)c(8 x 2) substrate, which is responsible for the formation of the ordered interface. The found surfaces provide a different platform to study the oxidation and properties of oxides, e. g., the origins of the photoemission shifts and electronic structures, using surface science methods.

  • 338. Punkkinen, M.P.J.
    et al.
    Hu, Q.-M.
    Kwon, S.K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Surface properties of 3d transition metals2011Ingår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 91, nr 27, s. 3627-3640Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.

  • 339. Qian, M. C.
    et al.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Mirbt, S.
    Atomic and electronic properties of anion vacancies on the (110) surfaces of InP, InAs, and InSb2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, nr 15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and the electronic structure of the anion vacancy on the (110) surfaces of InP, InAs, and InSb. An inward relaxation of the three neighboring In atoms next to the anion vacancy is obtained, but the stable atomic structure depends critically on the vacancy charge state. The +1 charged vacancy exhibits a nonsymmetric configuration with one rebonded dimer, while both 0 and -1 charged vacancies show a symmetric configuration with loosely rebonded and rebonded trimer, respectively. For InP and InAs, the charge-transfer levels epsilon(+1/0) and epsilon(0/-1) are located around the center of the band gap; whereas for InSb, the -1 charge state is stable in the whole band gap. In contrast to bulk, the surface vacancy is a positive-U center. The band structures and the density of states have been calculated. Three vacancy states, one deep in the valence band and two around the band gap, are identified. Our results show that the character of the vacancy states is mainly dependent on the atomic configuration.

  • 340. Qian, M. C.
    et al.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Mirbt, S.
    Structure of the P vacancy on the InP(110) surface from first principles2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have performed density functional theory (DFT) calculations to study the geometric structure of the phosphorus vacancy on the InP(110) surface. The stable structure of the P vacancy depends critically on its charge state. For a (+1) charged P vacancy, the nonsymmetric configuration with one rebonded dimer is favored, while the symmetric configuration shows a saddle point behavior. For a (-1) charged P vacancy, both the symmetric and nonsymmetric configurations are local minima, where the symmetric configuration has the lowest energy. Using the nudged elastic band method, we have determined the reaction path and energy barrier between two configurations for both (+1) and (-1) charged vacancies. The simulated scanning tunneling microscopy (STM) images of the P vacancy on p-type and n-type InP(110) surfaces are calculated and compared with the available experimental results. We support the point of view that the observed STM image of the P vacancy is an average result of thermal flipping between two possible configurations.

  • 341.
    Qian, Zhao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hudson, M. Sterlin Leo
    Raghubanshi, Himanshu
    Scheicher, Ralph H.
    Pathak, Biswarup
    Araujo, C. Moyses
    Blomqvist, Andreas
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Srivastava, O. N.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Excellent Catalytic Effects of Graphene Nanofibers on Hydrogen Release of Sodium alanate2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 20, s. 10861-10866Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled devices and vehicles remains hydrogen storage. More environmentally friendly and effective nonmetal catalysts are required to improve hydrogen sorption. In this paper, through a combination of experiment and theory, we evaluate and explore the catalytic effects of layered graphene nanofibers toward hydrogen release of light metal hydrides such as sodium alanate. Graphene nanofibers, especially the helical kind, are found to considerably improve hydrogen release from NaAlH4, which is of significance for the further enhancement of this practical material for environmentally friendly and effective hydrogen storage applications. Using density functional theory, we find that carbon sheet edges, regardless of whether they are of zigzag or armchair type, can weaken Al-H bonds in sodium alanate, which is believed to be due to a combination of NaAlH4 destabilization and dissociation product stabilization. The helical form of graphene nanofibers, with larger surface area and curved configuration, appears to benefit the functionalization of carbon sheet edges. We believe that our combined experimental and theoretical study will stimulate more explorations of other microporous or mesoporous nanomaterials with an abundance of exposed carbon edges in the application of practical complex light metal hydride systems.

  • 342.
    Qian, Zhao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Jiang, Xue
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    De Sarkar, Abir
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Adit Maark, Tuhina
    Deshpande, Mrinalini
    Bououdina, Mohamed
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Screening study of light-metal and transition-metal-doped NiTiH hydrides as Li-ion battery anode materials2014Ingår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 258, s. 88-91Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here we have investigated systematically the effects of various light-metals (Mg, Al) and transition-metals (V, Cr, Mn, Fe, Co, Cu, Zn) on the electrochemical properties of NiTiH hydrides as anodes for Li-ion battery applications. Based on the pristine NiTiH, a screening study in terms of the structure volume, average voltage and specific capacity has been performed to choose the most proper metal dopants. The most thermodynamically stable doping sites (Ni or Ti site) of various dopant metals have been determined respectively. It is finally summarized that in this study, the light metal Al or the transition metals Cr, Mn and Fe have the most comprehensive effects and are the most promising metal dopants for the pristine NiTiH hydride. This theoretical study is proposed to help understand the properties of the material and guide the design and development of more efficient metal-hydrides materials for Li-ion battery anode applications.

  • 343.
    Rahaman, Moshiour
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Finite tempreture elastic properties of B2-FeCo alloy: a first-principles studyManuskript (preprint) (Övrigt vetenskapligt)
  • 344.
    Rahaman, Moshiour
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    First-principles study of atomic ordering in fcc Ni-Cr alloys2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 6, s. 064103-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate atomic ordering in fcc Ni-rich Ni-Cr alloys using first-principles techniques and statistical mechanics simulations based on the Ising Hamiltonian with effective cluster interactions computed by the screened generalized perturbation method (SGPM) and projector augmented wave (PAW) method. We demonstrate that effective chemical interactions in this system are quite sensitive to alloy composition and in fact to the specific configurational state. The chemical interactions for the high-temperature random state produce the atomic short-range order (SRO) with intensity maximum close to the (2/3 2/3 0) point of the reciprocal space in agreement with the previous first-principles investigation. A consistent with diffuse neutron scattering data maximum at the (1 1/2 0) position is obtained onlywhenwe take into consideration relatively small strain-induced interactions, which solves a long-standing inconsistency between theory and experiment in this system. The calculated transition temperature of order-disorder transition of Ni2Cr alloy, 880 K, is in good agreement with the experimental value of 863 K.

  • 345.
    Rahaman, Moshiour
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Razumovskiy, Vsevolod
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Temperature dependence of stacking-fault and anti-phase boundary energies in Al3Sc from ab initio calculations2013Ingår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 93, nr 25, s. 3423-3441Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Temperature dependence of intrinsic stacking-fault energies (SFE) and anti-phase boundary energies (APBE) of AlSc is investigated in first-principles calculations using the axial Ising model and supercell approach. The temperature effect has been taken into consideration by including the one-electron thermal excitations in the electronic structure calculations, and vibrational free energy in the harmonic approximation as well as by using temperature dependent lattice constant. The latter has been determined within the Debye-Gruneisen model, which reproduces well the experimental data. The APBE and SFE are found to be reduced by about 10% in the temperature interval from 0 to 1000 K. It is shown that the inclusion of the free energy of lattice vibrations in the harmonic approximation increases the SFE further by about 4%. We also find a substantial contribution from local lattice relaxations in the case of APBE for the (111) plane and SFE leading to their reduction by about 30%.

  • 346.
    Rahaman, Moshiour
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mookerjee, Abhijit
    Johansson, Börje
    Magnetic state effect upon the order-disorder phase transition in Fe-Co alloys: A first-principles study2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 5, s. 054202-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the effect of global magnetization on the effective cluster interactions and order-disorder phase transition in FexCo1-x alloys. The effective cluster interactions are obtained by the screened generalized perturbation method as it is implemented in the exact muffin-tin orbitals formalism within the coherent potential approximation. The ordering transition from the high-temperature disordered body-centered cubic alloy to the ordered B2 phase is determined by Monte Carlo simulations. The calculated transition temperatures are in good agreement with the available experimental data for the effective interactions, which correspond to the experimentally observed magnetization at the order-disorder phase transition.

  • 347. Ravindran, P.
    et al.
    Kjekshus, A.
    Fjellvag, H.
    James, P.
    Nordstrom, L.
    Johansson, Börje
    Eriksson, O.
    Large magnetocrystalline anisotropy in bilayer transition metal phases from first-principles full-potential calculations2001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6314, nr 14Artikel, forskningsöversikt (Refereegranskat)
  • 348. Ravindran, P.
    et al.
    Kjekshus, A.
    Fjellvag, H.
    Puschnig, P.
    Ambrosch-Draxl, C.
    Nordstrom, L.
    Johansson, Börje
    Raman- and infrared-active phonons in superconducting and nonsuperconducting rare-earth transition-metal borocarbides from full-potential calculations2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, nr 10Artikel i tidskrift (Refereegranskat)
  • 349. Razumovskii, I. M.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Razumovskiy, Vsevolod I.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Logunov, A. V.
    Larionov, V. N.
    Ospennikova, O. G.
    Poklad, V. A.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    New generation of Ni-based superalloys designed on the basis of first-principles calculations2008Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 497, nr 1-2, s. 18-24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new approach to the design of Ni-based single crystal superalloys is proposed. It is based on a concept that under given structural conditions, the creep-rupture characteristics of superalloys are mainly determined by interatomic bonding given by the cohesive energy. In order to characterize the individual contribution of each alloying element to the strength properties at high temperature, we introduce a parameter, X, which is the partial molar cohesive energy of an alloy component. This parameter is then obtained in the total energy first-principles calculations for a usual set of alloying elements. We demonstrate that creep-rupture characteristics of alloys indeed correlate with the total gain partial molar cohesive energy due to alloying and find that W, Ta, and Re have the highest values of X, and should therefore play the major role in providing high-temperature strength of superalloys. Based on this finding, we design three new superalloys with a high content of W and show that they have superior creep-rupture properties compared not only with their counterparts with the lower content of W, but also with the best Ru-bearing Ni-based superalloys.

  • 350. Rekhi, S.
    et al.
    Dubrovinsky, L. S.
    Ahuja, R.
    Saxena, S. K.
    Johansson, Börje
    Experimental and theoretical investigations on eskolaite (Cr2O3) at high pressures2000Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 302, nr 02-jan, s. 16-20Artikel i tidskrift (Refereegranskat)
45678910 301 - 350 av 458
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf