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  • 251.
    Darakchieva, Vanya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hofmann, T.
    University of Nebraska-Lincoln, USA.
    Schubert, M.
    University of Nebraska-Lincoln, USA.
    Sernelius, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Giuliani, Finn
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Xie, Mengyao
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Persson, Per O. A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Schaff, W. J.
    Cornell University, Ithaca, NY, USA.
    Hsiao, C.-L.
    National Taiwan University, Taipei, Taiwan.
    Chen, L.-C.
    National Taiwan University, Taipei, Taiwan.
    Nanishi, Y
    Ritsumeikan University, Shiga, Japan.
    Unravelling the free electron behavior in InN2008Ingår i: Optoelectronic and Microelectronic Materials and Devices, 2008, IEEE , 2008, s. 90-97Konferensbidrag (Refereegranskat)
    Abstract [en]

    Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.

  • 252.
    Darakchieva, Vanya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Hofmann, T
    University of Nebraska.
    Schubert, M
    University of Nebraska.
    Sernelius, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Persson, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Giuliani, Finn
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Alves, E
    Sacavem, Portugal.
    Lu, H
    Cornell University.
    Schaff, W J
    Cornell University.
    Free electron behavior in InN: On the role of dislocations and surface electron accumulation2009Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 2, s. 022109-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN based devices.

  • 253.
    Darakchieva, Vanya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Xie, Mengyao
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Tasnadi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kamimura, J
    Sophia University.
    Kishino, K
    Japan Science & Technology Agency.
    Lattice parameters, deviations from Vegards rule, and E-2 phonons in InAlN2008Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, nr 26, s. 261908-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The lattice parameters of InxAl1-xN in the whole compositional range are studied using first-principle calculations. Deviations from Vegards rule are obtained via the bowing parameters, delta(a)=0.0412 +/- 0.0039 A and delta(c)=-0.060 +/- 0.010 A, which largely differ from previously reported values. Implications of the observed deviations from Vegards rule on the In content extracted from x-ray diffraction are discussed. We also combine these results with x-ray diffraction and Raman scattering studies on InxAl1-xN nanocolumns with 0.627 <= x <= 1 and determine the E-2 phonon frequencies versus In composition in the scarcely studied In-rich compositional range.

  • 254.
    Davidsson, Joel
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Orbital-free Density-Functional Theory in a Finite Element Basis2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this work, we have implemented an orbital-free density functional theory (OF-DFT) solver using the finite element method. In OF-DFT, the total ground state energy is minimized directly with respect to the electron density, rather than via orbitals like in the standard Kohn-Sham approach. For this to be possible, one needs an approximation of a universal density functional of the non-interacting kinetic energy. Presently available approximations allow for computation with very low computational expense, but which gives inaccurate energies. A stable OF-DFT code can be used as a testbed for new kinetic energy functionals and provide the necessary tool for investigating the accuracy of OF-DFT calculations for complex systems. We have implemented Thomas-Fermi theory with and without nuclear cusp condition, as well as additional exchange terms of Dirac and Amaldi. The program uses an extended version of the steepest descent in order to find the minimizing density in the variational principle. Our results include convergence tests for the hydrogen atom, weak bonding in the H2 molecule, and accurate results for the lightest noble gases (He, Ne, Ar). For heavier atoms (Kr, Xe, Rn), the results are less accurate. In addition, we consider hydrogen in the simple cubic structure without the cusp condition, which is a first attempt to use the code for periodic systems. Lastly, we discuss some possible improvements for the iterative process towards the minimizing density, as well as other possible directions for future development.

  • 255.
    Davidsson, Joel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ivády, Viktor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Nguyen, Son Tien
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    First principles predictions of magneto-optical data for semiconductor point defect identification: the case of divacancy defects in 4H-SiC2018Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, artikel-id 023035Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Study and design of magneto-optically active single point defects in semiconductors are rapidly growing fields due to their potential in quantum bit (qubit) and single photon emitter applications. Detailed understanding of the properties of candidate defects is essential for these applications, and requires the identification of the defects microscopic configuration and electronic structure. In multicomponent semiconductors point defects often exhibit several non-equivalent configurations of similar but different characteristics. The most relevant example of such point defect is the divacancy in silicon carbide, where some of the non-equivalent configurations implement room temperature qubits. Here, we identify four different configurations of the divacancy in 4H-SiC via the comparison of experimental measurements and results of first-principle calculations. In order to accomplish this challenging task, we carry out an exhaustive numerical accuracy investigation of zero-phonon line and hyperfine coupling parameter calculations. Based on these results, we discuss the possibility of systematic quantum bit search.

  • 256.
    Davidsson, Joel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ivády, Viktor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Nguyen, Son Tien
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Identification of divacancy and silicon vacancy qubits in 6H-SiC2019Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, nr 11, artikel-id 112107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Point defects in semiconductors are relevant for use in quantum technologies as room temperature qubits and single photon emitters. Among suggested defects for these applications are the negatively charged silicon vacancy and the neutral divacancy in SiC. The possible nonequivalent configurations of these defects have been identified in 4H-SiC, but for 6H-SiC, the work is still in progress. In this paper, we identify the different configurations of the silicon vacancy and the divacancy defects to each of the V1-V3 and the QL1-QL6 color centers in 6H-SiC, respectively. We accomplish this by comparing the results from ab initio calculations with experimental measurements for the zero-phonon line, hyperfine tensor, and zero-field splitting. Published under license by AIP Publishing.

  • 257.
    de Sousa, Leonardo Evaristo
    et al.
    Univ Brasilia, Brazil.
    Bueno, Fernando Teixeira
    Univ Brasilia, Brazil.
    da Silva Filho, Demetrio Antonio
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Dynamical exciton decay in organic materials: the role of bimolecular recombination2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 4, s. 1711-1716Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Excitons play a critical role in light emission when it comes to organic semiconductors. In high exciton concentration regimes, monomolecular and bimolecular routes for exciton recombination can yield different products affecting significantly the materials optical properties. Here, the dynamical decay of excitons is theoretically investigated using a kinetic Monte Carlo approach that addresses singlet exciton diffusion. Our numerical protocol includes two distinct exciton-exciton interaction channels: exciton annihilation and biexciton cascade emission. Our findings reveal that these channels produce different consequences concerning diffusion and spectroscopic properties, being able to explain diverging experimental observations. Importantly, we estimate critical exciton densities for which bimolecular recombination becomes dominant and investigate its effect on average exciton lifetimes and diffusion lengths.

  • 258.
    Dehant, Véronique
    et al.
    Royal Observatory of Belgium.
    Sargent, Anneila
    California Institute of Technology, USA.
    Walmsley, Malcolm C.
    Arcetri Observatory, Florence,Italy.
    Berggren, Karl-Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Edvardsson, David
    Vetenskapsrådet.
    International Evaluation of Onsala Space Observatory2010Rapport (Övrig (populärvetenskap, debatt, mm))
  • 259.
    Delange, Pascal
    et al.
    University of Paris Saclay, France.
    Ayral, Thomas
    CEA, France.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ferrero, Michel
    University of Paris Saclay, France; Coll France, France.
    Parcollet, Olivier
    CEA, France.
    Biermann, Silke
    University of Paris Saclay, France; Coll France, France.
    Pourovskii, Leonid
    University of Paris Saclay, France; Coll France, France; National University of Science and Technology MISIS, Russia.
    Large effects of subtle electronic correlations on the energetics of vacancies in alpha-Fe2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 10, s. 100102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the effect of electronic Coulomb correlations on the vacancy formation energy in paramagnetic alpha-Fe within ab initio dynamical mean-field theory. The calculated value for the formation energy is substantially lower than in standard density-functional calculations and in excellent agreement with experiment. The reduction is caused by an enhancement of electronic correlations at the nearest neighbors of the vacancy. This effect is explained by subtle changes in the corresponding spectral function of the d electrons. The local lattice relaxations around the vacancy are substantially increased by many-body effects.

  • 260.
    Deniz, Vivianne
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Boström, Mathias
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Bratko, D.
    Virginia Commonwealth University, Richmond USA.
    Tavares, F.W.
    Universidade Federal do Rio de Janeifo, Brazil.
    Ninham, B.W.
    Australian National University, Canberra, Australia.
    Specific ion effects: Interaction between nanoparticles in electrolyte solutions2008Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 319, s. 98-102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

       

  • 261.
    Dewandre, Antoine
    et al.
    University of Liege, Belgium.
    Hellman, Olle
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. CALTECH, CA 91125 USA.
    Bhattacharya, Sandip
    Ruhr University of Bochum, Germany.
    Romero, Aldo H.
    West Virginia University, WV 26506 USA; Benemerita University of Autonoma Puebla, Mexico.
    Madsen, Georg K. H.
    TU Wien, Austria.
    Verstraete, Matthieu J.
    University of Liege, Belgium.
    Two-Step Phase Transition in SnSe and the Origins of its High Power Factor from First Principles2016Ingår i: PHYSICAL REVIEW LETTERS, ISSN 0031-9007, Vol. 117, nr 27, artikel-id 276601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interest in improving the thermoelectric response of bulk materials has received a boost after it has been recognized that layered materials, in particular SnSe, show a very large thermoelectric figure of merit. This result has received great attention while it is now possible to conceive other similar materials or experimental methods to improve this value. Before we can now think of engineering this material it is important we understand the basic mechanism that explains this unusual behavior, where very low thermal conductivity and a high thermopower result from a delicate balance between the crystal and electronic structure. In this Letter, we present a complete temperature evolution of the Seebeck coefficient as the material undergoes a soft crystal transformation and its consequences on other properties within SnSe by means of first-principles calculations. Our results are able to explain the full range of considered experimental temperatures.

  • 262.
    Di Meo, Florent
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Pedersen, Morten
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan. University of Southern Denmark, Denmark.
    Rubio-Magnieto, Jenifer
    University of Mons UMONS, Belgium.
    Surin, Mathieu
    University of Mons UMONS, Belgium.
    Linares, Mathieu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan. University of Mons UMONS, Belgium.
    Norman, Patrick
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    DNA Electronic Circular Dichroism on the Inter-Base Pair Scale: An Experimental Theoretical Case Study of the AT Homo-Oligonucleotide2015Ingår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, nr 3, s. 355-359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A successful elucidation of the near-ultraviolet electronic circular dichroism spectrum of a short double-stranded DNA is reported. Time-dependent density functional theory methods are shown to accurately predict spectra and assign bands on the microscopic base-pair scale, a finding that opens the field for using circular dichroism spectroscopy as a sensitive nanoscale probe of DNA to reveal its complex interactions with the environment.

  • 263.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Shukla, P K
    Ruhr University Bochum.
    Stenflo, Lennart
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Simulation study of the filamentation of counter-streaming beams of the electrons and positrons in plasmas2009Ingår i: PLASMA PHYSICS AND CONTROLLED FUSION, ISSN 0741-3335, Vol. 51, nr 6, s. 065015-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The filamentation instability (FI) driven by two spatially uniform and counter-streaming beams of charged particles in plasmas is modelled by a particle-in-cell simulation. Each beam consists of electrons and positrons. The four species are equally dense and have the same temperature. The one-dimensional simulation direction is orthogonal to the beam velocity vector. The magnetic field grows spontaneously and rearranges the particles in space, such that the distributions of the electrons of one beam and the positrons of the second beam match. The simulation demonstrates that as a result no electrostatic field is generated by the magnetic field through its magnetic pressure gradient prior to its saturation. This electrostatic field would be repulsive at the centres of the filaments and limit the maximum charge and current density. The filaments of electrons and positrons in this simulation reach higher charge and current densities than in one with no positrons. The oscillations of the magnetic field strength induced by the magnetically trapped particles result in an oscillatory magnetic pressure gradient force. The latter interplays with the statistical fluctuations in the particle density and it probably enforces a charge separation, by which electrostatic waves grow after the FI has saturated.

  • 264.
    Dubrovinskaia, N.
    et al.
    Bayerisches Geoinstitut, Universität Bayreuth, Germany.
    Dubrovinsky, L.
    Bayerisches Geoinstitut, Universität Bayreuth.
    Crichton, W.A.
    European Synchrotron Radiation Facility, Grenoble.
    Zarechnaya, E.
    Moscow Insitute of Steel and Alloys, Moscow.
    Isaev, E.I.
    Moscow Institute of Steel and Alloys, Moscow.
    Abrikosov, Igor
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Compressibility of boron-doped diamond2006Ingår i: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 26, No. 2, s. 79-85Artikel i tidskrift (Refereegranskat)
  • 265.
    Dubrovinskaia, N.
    et al.
    Universität Bayreuth, Germany.
    Dubrovinsky, L.
    Universität Bayreuth, Germany.
    Kantor, I
    Universität Bayreuth, Germany.
    Crichton, W.A.
    European Synchrotron Radiation Facility, Grenoble.
    Dmitriev, V.
    Swiss-Norwegian Beam Lines at ESRF, Grenoble.
    Prakapenka, V.
    University of Chicago, USA.
    Shen, G.
    University of Chicago.
    Vitros, L.
    Uppsala University, KTH, Stockholm.
    Ahuga, R.
    Uppsala University.
    Johansson, B.
    Uppsala University, KTH Stockholm.
    Abrikosov, Igor
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Beating the Miscibility Barrier Between Iron Group Elements and Magnesium by High-Pressure Alloying2005Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 86, s. 245502-245513Artikel i tidskrift (Refereegranskat)
  • 266.
    Dubrovinsky, L.
    et al.
    University of Bayreuth, Germany.
    Dubrovinskaia, N.
    University of Bayreuth, Germany.
    Bykova, E.
    University of Bayreuth, Germany; University of Bayreuth, Germany.
    Bykov, M.
    University of Bayreuth, Germany.
    Prakapenka, V.
    University of Chicago, IL 60437 USA.
    Prescher, C.
    University of Chicago, IL 60437 USA.
    Glazyrin, K.
    Deutsch Elektronen Synchrotron DESY, Germany.
    Liermann, H. -P.
    Deutsch Elektronen Synchrotron DESY, Germany.
    Hanfland, M.
    European Synchrotron Radiat Facil, France.
    Ekholm, Marcus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Feng, Qingguo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Pourovskii, L. V.
    Linköpings universitet, Tekniska fakulteten. Ecole Polytech, France.
    Katsnelson, M. I.
    Radboud University of Nijmegen, Netherlands; Ural Federal University, Russia.
    Wills, J. M.
    Los Alamos National Lab, NM 87545 USA.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. National University of Science and Technology MISIS, Russia.
    The most incompressible metal osmium at static pressures above 750 gigapascals2015Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 525, nr 7568, s. 226-+Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metallic osmium (Os) is one of the most exceptional elemental materials, having, at ambient pressure, the highest known density and one of the highest cohesive energies and melting temperatures(1). It is also very incompressible(2-4), but its high-pressure behaviour is not well understood because it has been studied(2-6) so far only at pressures below 75 gigapascals. Here we report powder X-ray diffraction measurements on Os at multi-megabar pressures using both conventional and double-stage diamond anvil cells(7), with accurate pressure determination ensured by first obtaining self-consistent equations of state of gold, platinum, and tungsten in static experiments up to 500 gigapascals. These measurements allow us to show that Os retains its hexagonal close-packed structure upon compression to over 770 gigapascals. But although its molar volume monotonically decreases with pressure, the unit cell parameter ratio of Os exhibits anomalies at approximately 150 gigapascals and 440 gigapascals. Dynamical mean-field theory calculations suggest that the former anomaly is a signature of the topological change of the Fermi surface for valence electrons. However, the anomaly at 440 gigapascals might be related to an electronic transition associated with pressure-induced interactions between core electrons. The ability to affect the core electrons under static high-pressure experimental conditions, even for incompressible metals such as Os, opens up opportunities to search for new states of matter under extreme compression.

  • 267.
    Dubrovinsky, L.
    et al.
    Bayerisches Geoinstitut, Universität Bayreuth, Germany.
    Dubrovinskaia, N.
    Mineralogical Institute Heidelberg University.
    Narygina, O.
    Bayerisches Geoinstitut Universität Bayreuth, Germany.
    Kantor, I.
    Bayerisches Geoinstitut Universität Bayreuth, Germany.
    Kuznetzov, A.
    Center for Advanced Radiation Sources, University of Chicago.
    Prakapenka, V. B.
    Center for Advanced Radiation Sources University of Chicago.
    Vitos, L.
    Research Institute for Solid State Physics and Optics, Budapest, Hungary.
    Johansson, B.
    Department of Physics Uppsala University.
    Mikhaylushkin, Arkady
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Simak, Sergey
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Abrikosov, Igor
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Body-Centered Cubic Iron-Nickel Alloy in Earth's Core2007Ingår i: Science / American Association for the Advancement of Science, Vol. Vol. 316. no. 5833, s. 1880-1883Artikel i tidskrift (Refereegranskat)
  • 268.
    Dufåker, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Karlsson, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Dimastrodonato, V
    Tyndall National Institute, University College Cork, Ireland.
    O Mereni, L
    Tyndall National Institute, University College Cork, Ireland.
    Sernelius, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Holtz, Per-Olof
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Pelucchi, E
    Tyndall National Institute, University College Cork, Ireland.
    Phonon replicas of charged and neutral exciton complexes in single quantum dots2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The longitudinal-optical (LO)-phonon coupling is experimentally examined by the optical decay of various charged and neutral exciton species in single quantum dots, and the related Huang-Rhys parameters are extracted. A positive trion exhibits significantly weaker LO-phonon replicas in the photoluminescence spectrum than the neutral and negatively charged species. Model computations show that the strength of the replicas is determined by the Coulomb interactions between electrons and holes, which modify the localization of the envelope wave functions and the net charge distribution.

  • 269.
    Edström, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Sangiovanni, Davide G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys2014Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, nr Part 1, s. 145-153Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Improved toughness is one of the central goals in the development of wear-resistant coatings. Previous studies of toughness in transition metal nitride alloys have addressed the effects of chemical composition in these compounds. Herein, we use density functional theory to study the effects of various metal sublattice configurations, ranging from fully ordered to fully disordered, on the mechanical properties of VM2N and TiM2N (M2 = W, Mo) ternary alloys. Results show that all alloys display high incompressibility, indicating strong M-N bonds. Disordered atomic arrangements yield lower values of bulk moduli and C11 elastic constants, as well as higher values of C44 elastic constants, compared to ordered structures. We attribute the low C44 values of ordered structures to the formation of fully-bonding states perpendicular to the applied stress. We find that the ductility of these compounds is primarily an effect of the increased valence electron concentration induced upon alloying.

  • 270.
    Edström, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr University of Bochum, Germany.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. University of Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. University of Illinois, IL 61801 USA.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Effects of incident N atom kinetic energy on TiN/TiN(001) film growth dynamics: A molecular dynamics investigation2017Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, nr 2, artikel-id 025302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200 K, a temperature within the optimal range for epitaxial TiN growth, with an incident N-to-Ti flux ratio of four, are carried out using incident N energies E-N = 2 and 10 eV and incident Ti energy E-Ti = 2 eV. To further highlight the effect of E-N, we grow a bilayer film with E-N = 2 eV initially and then switch to E-N = 10 eV. As-deposited layers are analyzed as a function of composition, island-size distribution, island-edge orientation, and vacancy formation. Results show that growth with E-N = 2 eV results in films that are globally overstoichiometric with islands bounded by N-terminated polar 110 edges, whereas films grown with E-N = 10 eV are flatter and closer to stoichiometric. However, E-N = 10 eV layers exhibit local N deficiency leading to the formation of isolated 111-oriented islands. Films grown by changing the incident energy from 2 to 10 eV during growth are more compact than those grown entirely with E-N = 2 eV and exhibit greatly reduced concentrations of upper-layer adatoms, admolecules, and small clusters. Islands with 110 edges formed during growth with E-N = 2 eV transform to islands with 100 edges as E-N is switched to 10 eV. Published by AIP Publishing.

  • 271.
    Edström, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Elastic properties and plastic deformation of TiC- and VC-based alloys2018Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 144, s. 376-385Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transition-metal (TM) carbides are an important class of hard, protective coating materials; however, their brittleness often limits potential applications. We use density functional theory to investigate the possibility of improving ductility by forming pseudobinary cubic (MMC)-M-1-C-2 alloys, for which M-1 = Ti or V and M-2 = W or Mo. The alloying elements are chosen based on previous results showing improved ductility of the corresponding pseudobinary nitride alloys with respect to their parent compounds. While commonly-used empirical criteria do not indicate enhanced ductility in the carbide alloys, calculated stress/strain curves along known slip systems, supported by electronic structure analyses, indicate ductile behavior for VMoC. As VMoC layers are sheared along the 1 (1) over bar0 direction on {111} planes, the stress initially increases linearly up to a yield point where the accumulated stress is partially dissipated. With further increase in strain, the stress increases again until fracture occurs. A similar mechanical behavior is observed for the corresponding TM nitride VMoN, known to be a ductile ceramic material [1]. Thus, our results show that VMoC is a TM carbide alloy which may be both hard and ductile, i.e. tough. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 272.
    Edström, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. University of Illinois, IL 61801 USA; University of Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. University of Illinois, USA.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth2016Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, nr 4, s. 041509-1-041509-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200K are carried out using incident flux ratios N/Ti -1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti-1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti=2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti-4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i. e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti-1 due to the formation and subsequent desorption of N-2 molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti-4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti-2 films, which have smoother surfaces, is closer to layer-by-layer. (C) 2016 American Vacuum Society.

  • 273.
    Edström, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Orebro Univ, Sweden.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    TiN film growth on misoriented TiN grains with simultaneous low-energy bombardment: Restructuring leading to epitaxy2019Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, artikel-id 137380Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We perform large-scale molecular dynamics simulations of TiN deposition at 1200 K on TiN substrates consisting of under-stoichiometric (N/Ti = 0.86) misoriented grains. The energy of incoming Ti atoms is 2 eV and that of incoming N atoms is 10 eV. The simulations show that misoriented grains are reoriented during the early stages of growth, after which the film grows 001 epitaxially and is nearly stoichiometric. The grain reorientation coincides with an increase in film N/Ti ratio. As the grains reorient, additional nitrogen can no longer be accommodated, and the film composition becomes stoichiometric as the overlayer grows epitaxially.

    Publikationen är tillgänglig i fulltext från 2021-06-20 11:38
  • 274.
    Edström, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Orebro Univ, Sweden.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Landälv, Ludvig
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Sandvik Coromant AB, Sweden.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Mechanical properties of VMoNO as a function of oxygen concentration: Toward development of hard and tough refractory oxynitrides2019Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, nr 6, artikel-id 061508Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl-structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem that may compromise material properties and performance. Here, the authors explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx solid solutions as a function of the oxygen concentration x. Elastic constant and intrinsic hardness calculations show that oxidation does not degrade the mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate that the presence of oxygen reduces the covalent bond character, which slightly lowers the alloy strength and intrinsic hardness. Nevertheless, the character of metallic d-d states, which are crucial for allowing plastic deformation and enhancing toughness, remains unaffected. Overall, the authors results suggest that VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high intrinsic hardness, while still being ductile. Published by the AVS.

  • 275.
    Ehn, Jonas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Propagation of Radio Waves in a Realistic Environment using a Parabolic Equation Approach2019Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Radars are used for range estimation of distant objects. They operate on the principle of sending electromagnetic pulses that are reflected off a target. This leads to the propagation of electromagnetic waves over large distances. As the waves propagate, they are affected by several aspects that decrease the performance of the radar system. In this master thesis, we derive a mathematical model that describes electromagnetic propagation in the troposphere. The model developed is based on a parabolic equation and uses the split-step Fourier method for its numerical solution. Using the model, we estimate the influence of a varying, complex, refractive index of the atmosphere, different lossy materials in the ground, terrain, and oceans. The terrain is described using a piecewise linear shift map method. The modelling of the ocean is done using a novel model which is a combination of terrain for large swells and Miller surface roughness for smaller waves, both based on a Pierson-Moskowitz sea spectrum. The model is validated and found to agree very well, with results found in the literature.

  • 276.
    Ekeroth, Sebastian
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Ikeda, Shuga
    Department of Intelligent Mechanical Systems, Tokyo Metropolitan University, Tokyo, Japan.
    Boyd, Robert
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Shimizu, Tetsuhide
    Department of Intelligent Mechanical Systems, Tokyo Metropolitan University, Tokyo, Japan.
    Helmersson, Ulf
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Impact of nanoparticle magnetization on the 3D formation of dual-phase Ni/NiO nanoparticle-based nanotrusses2019Ingår i: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 21, nr 11, artikel-id 21:228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic nanoparticles with average size 30 nm were utilized to build three-dimensional framework structures—nanotrusses. In dual-phase Ni/NiO nanoparticles, there is a strong correlation between the amount of magnetic Ni and the final size and shape of the nanotruss. As it decreases, the length of the individual nanowires within the trusses also decreases, caused by a higher degree of branching of the wires. The position and orientation of the non-magnetic material within the truss structure was also investigated for the different phase compositions. For lower concentrations of NiO phase, the electrically conducting Ni-wire framework is maintained through the preferential bonding between the Ni crystals. For larger concentrations of NiO phase, the Ni-wire framework is interrupted by the NiO. The ability to use nanoparticles that are only partly oxidized in the growth of nanotruss structures is of great importance. It opens the possibility for using not only magnetic metals such as pure Ni, Fe, and Co, but also to use dual-phase nanoparticles that can strongly increase the efficiency of e.g. catalytic electrodes and fuel cells.

  • 277.
    Ekeroth, Sebastian
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Boyd, Robert
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Ekspong, Joakim
    Umeå Univ, Sweden.
    Wågberg, Thomas
    Umeå Univ, Sweden.
    Edman, Ludvig
    Umeå Univ, Sweden.
    Brenning, Nils
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten. KTH Royal Inst Technol, Sweden.
    Helmersson, Ulf
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma2018Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, nr 5, s. 3132-3137Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 mu m thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H-2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm(2).

  • 278.
    Ekholm, Marcus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Theoretical Descriptions of Complex Magnetism in Transition Metals and Their Alloys2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis, various methods for studying solids by simulations of quantummechanical equations, have been applied to transition metals and their alloys. Transition metals such as Fe, Ni, and Mn, are not only cornerstones in modern technology, but also key components in the very fabric of the Earth interior. Such systems show highly complex magnetic properties. As shown within this thesis, to understand and predict their properties from a microscopic level, is still a highly demanding task for the the quantum theory of solids. This is especially crucial at elevated temperature and pressure.

    It is found that the magnetic degrees of freedom are inseparable from the structural, elastic and chemical properties of such alloy systems. This requires theoretical descriptions capable of handling this interplay. Such schemes are discussed and demonstrated.

    Furthermore, the importance of the description of Coulomb correlation effects is demonstrated by DFT calculations and also by going beyond the one-electron description by the LDA+DMFT method.

    It is also shown how magnetic interactions in the half-metallic compound NiMnSb can be manipulated by alloying. The stability of these alloys is  also evaluated in calculations, and verified by experimental synthesis at ambient conditions.

    Delarbeten
    1. Structural and magnetic ground-state properties of gamma-FeMn alloys from ab initio calculations
    Öppna denna publikation i ny flik eller fönster >>Structural and magnetic ground-state properties of gamma-FeMn alloys from ab initio calculations
    2011 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 10, s. 104423-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The magnetic properties of fcc-FeMn alloys, especially at the Fe(0.5)Mn(0.5) composition, have been the subject of intense experimental and theoretical investigations for several decades. We carry out an ab initio theoretical study of this system, including simultaneous optimization of structural and magnetic properties, and find that the ground state is the locally relaxed noncollinear 3Q antiferromagnetic structure. We also show that the two most frequently used parameterizations of the generalized gradient approximation not only fail to reproduce the equilibrium lattice constant of FeMn alloys, and consequently the magnetic properties, but also internally yield qualitatively different results. For practical studies of these alloys, which currently attract great attention, we propose a set of approximations, which is internally consistent, and brings the equilibrium lattice constant and magnetic properties in good agreement with the experiment in the whole range of alloy compositions.

    Ort, förlag, år, upplaga, sidor
    American Physical Society, 2011
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-71074 (URN)10.1103/PhysRevB.84.104423 (DOI)000294922100002 ()
    Anmärkning
    Funding Agencies|Goran Gustafsson Foundation for Research in Natural Sciences and Medicine||Swedish e-Science Research Centre (SeRC)||Tillgänglig från: 2011-09-30 Skapad: 2011-09-30 Senast uppdaterad: 2017-12-08
    2. Influence of chemical composition and magnetic effects on the elastic properties of fcc Fe-Mn alloys
    Öppna denna publikation i ny flik eller fönster >>Influence of chemical composition and magnetic effects on the elastic properties of fcc Fe-Mn alloys
    Visa övriga...
    2011 (Engelska)Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, nr 4, s. 1493-1501Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The influence of the Mn content on the elastic properties of face centered cubic Fe-Mn alloys was studied using the combinatorial approach. Fe-Mn thin films with a graded chemical composition were synthesized. Nanoindentation experiments were carried out to investigate the elastic properties as a function of the Mn content. As the Mn content increases from similar to 23 to similar to 39 at.%, the average bulk modulus varies from 143 to 105 GPa. Ab initio calculations served to probe the impact of magnetic effects on the elastic properties. The magnetic state description with disordered local moments yields the best agreement with the experimental results, whereas with non-magnetic and antiferromagnetic configurations the bulk modulus is overestimated. The strong impact of the magnetic configuration may be understood based on the differences in the chemical bonding and the magnetovolume effect. It is suggested that, owing to minute energy differences of competing antiferromagnetic configurations, a mixture of these with a "notional magnetic disorder" is present, which is in fact well described by the disordered local moments model. These results show that the combinatorial thin film synthesis with subsequent nanoindentation is an appropriate tool for investigating the elastic properties of Fe-Mn alloys systematically as a function of the chemical composition, to validate theoretical models.

    Ort, förlag, år, upplaga, sidor
    Elsevier Science B.V., Amsterdam., 2011
    Nyckelord
    Iron alloys, Sputtering, Elastic properties, Ab initio calculations, Nanoindentation
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-66331 (URN)10.1016/j.actamat.2010.11.013 (DOI)000287265100018 ()
    Tillgänglig från: 2011-03-11 Skapad: 2011-03-11 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    3. Ab initio lattice stability of fcc and hcp Fe-Mn random alloys
    Öppna denna publikation i ny flik eller fönster >>Ab initio lattice stability of fcc and hcp Fe-Mn random alloys
    Visa övriga...
    2010 (Engelska)Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, nr 29, s. 295402-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We have studied the lattice stability of face centred cubic (fcc) versus hexagonal close packed (hcp) Fe-Mn random alloys using ab initio calculations. In the calculations we considered the antiferromagnetic order of local moments, which for fcc alloys models the magnetic configuration of this phase at room temperature (below its Neel temperature) as well as their complete disorder, corresponding to paramagnetic fcc and hcp alloys. For both cases, the results are consistent with our thermodynamic calculations, obtained within the Calphad approach. For the room temperature magnetic configuration, the cross-over of the total energies of the hcp phase and the fcc phase of Fe-Mn alloys is at the expected Mn content, whereas for the magnetic configuration above the fcc Neel temperature, the hcp lattice is more stable within the whole composition range studied. The increase of the total energy difference between hcp and antiferromagnetic fcc due to additions of Mn as well as the stabilizing effect of antiferromagnetic ordering on the fcc phase are well displayed. These results are of relevance for understanding the deformation mechanisms of these random alloys.

    Ort, förlag, år, upplaga, sidor
    Iop Publishing Ltd, 2010
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-58224 (URN)10.1088/0953-8984/22/29/295402 (DOI)000279616000012 ()
    Tillgänglig från: 2010-08-10 Skapad: 2010-08-09 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
    4. The influence of additions of Al and Si on the lattice stability of fcc and hcp Fe-Mn random alloys
    Öppna denna publikation i ny flik eller fönster >>The influence of additions of Al and Si on the lattice stability of fcc and hcp Fe-Mn random alloys
    Visa övriga...
    2011 (Engelska)Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, nr 24, s. 246003-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We have studied the influence of additions of Al and Si on the lattice stability of face-centred-cubic (fcc) versus hexagonal-closed-packed (hcp) Fe-Mn random alloys, considering the influence of magnetism below and above the fcc Neel temperature. Employing two different ab initio approaches with respect to basis sets and treatment of magnetic and chemical disorder, we are able to quantify the predictive power of the ab initio methods. We find that the addition of Al strongly stabilizes the fcc lattice independent of the regarded magnetic states. For Si a much stronger dependence on magnetism is observed. Compared to Al, almost no volume change is observed as Si is added to Fe-Mn, indicating that the electronic contributions are responsible for stabilization/destabilization of the fcc phase.

    Ort, förlag, år, upplaga, sidor
    Iop Publishing Ltd, 2011
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-69173 (URN)10.1088/0953-8984/23/24/246003 (DOI)000291152500019 ()
    Tillgänglig från: 2011-06-17 Skapad: 2011-06-17 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    5. Elastic properties of fcc Fe-Mn-X (X = Al, Si) alloys studied by theory and experiment
    Öppna denna publikation i ny flik eller fönster >>Elastic properties of fcc Fe-Mn-X (X = Al, Si) alloys studied by theory and experiment
    Visa övriga...
    2011 (Engelska)Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, nr 8, s. 3145-3155Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We have studied the influence of Al and Si additions on the elastic properties of face-centered cubic (fcc) Fe-Mn random alloys with Fe/Mn ratios of 4.00 and 2.33 using ab initio calculations. When Al is added up to 8 at.% the shearing elastic constants (C-11-C-12)/2 and C-44 decrease, resulting in a drop of similar to 20% in shear and similar to 19% in Youngs modulus. In fcc Fe-Mn-Si alloys, the trends in the elastic constants are similar, but less drastic, with a similar to 7% shear and similar to 6% Youngs modulus decrease when Si is added up to 8 at.%. The Fe/Mn ratio exhibits a minor influence on the shear and Youngs modulus values at constant Al and Si contents. To assess the quality of the ab initio data Fe-Mn-Al and Fe-Mn-Si thin films with an fcc structure were combinatorially synthesized and the elastic properties measured using nanoindentation. For both systems the measured and calculated lattice parameters are in good agreement. Although the measured Youngs modulus data showed significant scatter due to the high surface roughness, they are in good agreement with the predicted values. For the Fe-Mn-Al system the calculations generally underestimate the experimental data by similar to 15%. For the Fe-Mn-Si system the calculated data are in general lower by similar to 10% than the experimentally determined values. The presented results are of relevance for multicomponent alloy design, since the effect of Si and Al addition on the elastic properties of Fe-Mn alloys can be predicted based on ab initio data.

    Ort, förlag, år, upplaga, sidor
    Elsevier Science B.V., Amsterdam., 2011
    Nyckelord
    Iron alloys, Sputtering, Elastic properties, Ab initio calculations, Nanoindentation
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-68186 (URN)10.1016/j.actamat.2011.01.054 (DOI)000290053100024 ()
    Tillgänglig från: 2011-05-13 Skapad: 2011-05-13 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    6. Supercell Calculations of Hyperfine Interactions in Transition-Metal Alloys
    Öppna denna publikation i ny flik eller fönster >>Supercell Calculations of Hyperfine Interactions in Transition-Metal Alloys
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We have performed calculations for the hyperfine field in the disordered Fe0.5Ni0.5 alloy using supercells with up to 864 atoms. The computational scheme is based on exact muffin-tin orbitals and the locally self-consistent Green’s function formalism, which scales linearly with the number of atoms in the supercell. This scheme allows local environment effects, such as chemical and magnetic environment, and short-range order, to be explicitly included. Supercell calculations for Fe-Ni show that while the average fields coincides with that obtained using the coherent potential approximation, there is a significant distribution of the hyperfine fields depending on the local environment. The fields of Fe and Ni show qualitatively different behaviour as a function of the on-site magnetic moment, but scale linearly with the average magnetic moment in the first coordination shell.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-78774 (URN)
    Tillgänglig från: 2012-06-20 Skapad: 2012-06-20 Senast uppdaterad: 2015-08-19Bibliografiskt granskad
    7. Importance of Thermally Induced Magnetic Excitations in First-principles Simulations of Elastic Properties of Transition Metal Alloys
    Öppna denna publikation i ny flik eller fönster >>Importance of Thermally Induced Magnetic Excitations in First-principles Simulations of Elastic Properties of Transition Metal Alloys
    2012 (Engelska)Ingår i: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 190, s. 291-294Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We demonstrate the importance of accounting for the complex magnetic ground state and finite temperature magnetic excitations in theoretical simulations of structural and elastic properties of transition metal alloys. Considering Fe72Cr16Ni12 face centered cubic (fcc) alloy, we compare results of first-principles calculations carried out for ferromagnetic and non-magnetic states, as well as for the state with disordered local moments. We show that the latter gives much more accurate description of the elastic properties for paramagnetic alloys. We carry out a determination of the magnetic ground state for fcc Fe-Mn alloys, considering collinear, as well as non-collinear states, and show the sensitively of structural and elastic properties in this system to the detailed alignment between magnetic moments. We therefore conclude that it is essential to develop accurate models of the magnetic state for the predictive description of properties of transition metal alloys.

    Nyckelord
    Magnetic transition metal alloys, magnetic ground state, disordered local moments, elastic properties, first-principles simulations
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-78775 (URN)10.4028/www.scientific.net/SSP.190.291 (DOI)000308061600070 ()
    Tillgänglig från: 2012-06-20 Skapad: 2012-06-20 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    8. Influence of the Magnetic State on the Chemical Order-Disorder Transition Temperature in Fe-Ni Permalloy
    Öppna denna publikation i ny flik eller fönster >>Influence of the Magnetic State on the Chemical Order-Disorder Transition Temperature in Fe-Ni Permalloy
    Visa övriga...
    2010 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 16, s. 167208-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Ort, förlag, år, upplaga, sidor
    American Physical Society, 2010
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-61178 (URN)10.1103/PhysRevLett.105.167208 (DOI)000283056100008 ()
    Anmärkning
    Original Publication: Marcus Ekholm, H Zapolsky, A V Ruban, I Vernyhora, D Ledue and Igor Abrikosov, Influence of the Magnetic State on the Chemical Order-Disorder Transition Temperature in Fe-Ni Permalloy, 2010, PHYSICAL REVIEW LETTERS, (105), 16, 167208. http://dx.doi.org/10.1103/PhysRevLett.105.167208 Copyright: American Physical Society http://www.aps.org/Tillgänglig från: 2010-11-08 Skapad: 2010-11-05 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
    9. Importance of correlation effects in hcp iron revealed by a pressure-induced electronic topological transition
    Öppna denna publikation i ny flik eller fönster >>Importance of correlation effects in hcp iron revealed by a pressure-induced electronic topological transition
    Visa övriga...
    2013 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, nr 11Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We discover that hcp phases of Fe and Fe0.9Ni0.1 undergo an electronic topological transition at pressures of about 40 GPa. This topological change of the Fermi surface manifests itself through anomalous behavior of the Debye sound velocity, c/a lattice parameter ratio, and Mossbauer center shift observed in our experiments. First-principles simulations within the dynamic mean field approach demonstrate that the transition is induced by many-electron effects. It is absent in one-electron calculations and represents a clear signature of correlation effects in hcp Fe. DOI: 10.1103/PhysRevLett.110.117206

    Ort, förlag, år, upplaga, sidor
    American Physical Society, 2013
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-78777 (URN)10.1103/PhysRevLett.110.117206 (DOI)000316172500027 ()
    Anmärkning

    Funding Agencies|Swedish e-Science Research Centre (SeRC)||Swedish Research Council|621-2011-4426|Swedish Foundation for Strategic Research (SSF) programs SRL Grant|10-0026|German Science Foundation (DFG)||German Ministry for Education and Research (BMBF)||National Science Foundation-Earth Sciences|EAR-1128799|Department of Energy-Geosciences|DE-FG02-94ER14466|U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences|DE-AC02-06CH11357|

    Tillgänglig från: 2012-06-20 Skapad: 2012-06-20 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    10. Configurational thermodynamics of Fe-Ni alloys at Earths core conditions
    Öppna denna publikation i ny flik eller fönster >>Configurational thermodynamics of Fe-Ni alloys at Earths core conditions
    Visa övriga...
    2011 (Engelska)Ingår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 308, nr 1-2, s. 90-96Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    By means of ab-initio calculations, we perform an analysis of the configurational thermodynamics, effects of disorder, and structural energy differences in Fe-Ni alloys at the pressure and temperature conditions of the Earths core. We show from ab-initio calculations that the ordering energies of fcc and hcp-structured Fe-Ni solid solutions at these conditions depend sensitively on the alloy configuration, i.e., on the degree of chemical disorder, and are on a scale comparable with the structural energy differences. From configurational thermodynamic simulations we find that a distribution of Fe and Ni atoms in the solutions should be very close to completely disordered at these conditions. Using this model of the Fe-Ni system, we have calculated the fcc-hcp structural free energy difference in a wide pressure-temperature range of 120-360 GPa and 1000-6600K. Our calculations show that alloying of Fe with Ni below 3000 K favours stabilisation of the fcc phase over the hcp, in agreement with experiments. However, above 3000 K the effect is reversed, and at conditions corresponding to those of the Earths inner core, Ni acts as an agent to stabilise the hcp phase.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2011
    Nyckelord
    Earths inner core, Fe-Ni alloy, ab-initio calculations, crystal structure
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-70218 (URN)10.1016/j.epsl.2011.05.035 (DOI)000293486100009 ()
    Anmärkning
    Original Publication: Marcus Ekholm, Arkady Mikhaylushkin, Sergey Simak, B Johansson and Igor Abrikosov, Configurational thermodynamics of Fe-Ni alloys at Earths core conditions, 2011, Earth and Planetary Science Letters, (308), 1-2, 90-96. http://dx.doi.org/10.1016/j.epsl.2011.05.035 Copyright: Elsevier http://www.elsevier.com/Tillgänglig från: 2011-08-26 Skapad: 2011-08-26 Senast uppdaterad: 2017-12-08Bibliografiskt granskad
    11. Energetics and magnetic impact of 3d-metal doping of the half-metallic ferromagnet NiMnSb
    Öppna denna publikation i ny flik eller fönster >>Energetics and magnetic impact of 3d-metal doping of the half-metallic ferromagnet NiMnSb
    2008 (Engelska)Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 77, nr 14, s. 144414-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We have performed a theoretical study of the effect of doping the half-Heusler alloy NiMnSb with the magnetic 3d metals Cr, Mn, Fe, Co, and Ni, with respect to both energetics and magnetic properties. Starting from the formation energies, we discuss the possibility of placing the dopant on different crystallographic positions in the alloy. We calculate total and local magnetic moments, effective exchange interactions, and density of states and also outline strategies to tune the magnetic properties of the alloy. Doping of NiMnSb with Cr as well as substituting some Ni with extra Mn have the largest impact on magnetic interactions in the system while preserving its half-metallic property. Therefore, we suggest the possibility that these dopants increase the thermal stability of half-metallicity in NiMnSb, with implications for its possible usage in spintronics applications.

    Nyckelord
    NiMnSb, spintronics, half-metallic, doping, defects
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-60433 (URN)10.1103/PhysRevB.77.144414 (DOI)
    Tillgänglig från: 2010-10-13 Skapad: 2010-10-13 Senast uppdaterad: 2017-12-12
    12. Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni1-xMn1+xSb
    Öppna denna publikation i ny flik eller fönster >>Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni1-xMn1+xSb
    Visa övriga...
    2010 (Engelska)Ingår i: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979, Vol. 108, nr 9Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We perform a combined theoretical and experimental study of the phase stability and magnetism of the off-stoichiometric Ni1-xMn1+xSb in the half-Heusler crystal phase. Our work is motivated by the need for strategies to engineer the magnetism of potentially half-metallic materials, such as NiMnSb, for improved performance at elevated temperatures. By means of ab initio calculations we investigate Ni1-xMn1+xSb over the whole composition range 0 andlt;= x andlt;= 1 of Ni replacing Mn and show that at relevant temperatures, the half-Heusler phase should be thermodynamically stable up to at least x=0.20 with respect to the competing C38 structure of Mn2Sb. Furthermore we find that half-Heusler Ni1-xMn1+xSb retains half-metallic band structure over the whole concentration range and that the magnetic moments of substitutional Mn-Ni atoms display magnetic exchange interactions an order of magnitude larger than the Ni-Mn interaction in NiMnSb. We also demonstrate experimentally that the alloys indeed can be created by synthesizing off-stoichiometric Ni1-xMn1+xSb films on MgO substrates by means of magnetron sputtering.

    Ort, förlag, år, upplaga, sidor
    American Institute of Physics, 2010
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-63149 (URN)10.1063/1.3476282 (DOI)000284270900068 ()
    Anmärkning
    Original Publication: Marcus Ekholm, Petter Larsson, Björn Alling, Ulf Helmersson and Igor Abrikosov, Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni1-xMn1+xSb, 2010, JOURNAL OF APPLIED PHYSICS, (108), 9, 093712. http://dx.doi.org/10.1063/1.3476282 Copyright: American Institute of Physics http://www.aip.org/Tillgänglig från: 2010-12-13 Skapad: 2010-12-13 Senast uppdaterad: 2015-08-19Bibliografiskt granskad
  • 279.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Structural and magnetic ground-state properties of gamma-FeMn alloys from ab initio calculations2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 10, s. 104423-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The magnetic properties of fcc-FeMn alloys, especially at the Fe(0.5)Mn(0.5) composition, have been the subject of intense experimental and theoretical investigations for several decades. We carry out an ab initio theoretical study of this system, including simultaneous optimization of structural and magnetic properties, and find that the ground state is the locally relaxed noncollinear 3Q antiferromagnetic structure. We also show that the two most frequently used parameterizations of the generalized gradient approximation not only fail to reproduce the equilibrium lattice constant of FeMn alloys, and consequently the magnetic properties, but also internally yield qualitatively different results. For practical studies of these alloys, which currently attract great attention, we propose a set of approximations, which is internally consistent, and brings the equilibrium lattice constant and magnetic properties in good agreement with the experiment in the whole range of alloy compositions.

  • 280.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Gambino, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Jönsson, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Tasnadi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Max Planck Inst Eisenforsch GmbH, Germany.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Assessing the SCAN functional for itinerant electron ferromagnets2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 9, artikel-id 094413Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory is a standard model for condensed-matter theory and computational material science. The accuracy of density functional theory is limited by the accuracy of the employed approximation to the exchange-correlation functional. Recently, the so-called strongly constrained appropriately normed (SCAN) [Sun, Ruzsinszky, and Perdew, Phys. Rev. Lett. 115, 036402 (2015)] functional has received a lot of attention due to promising results for covalent, metallic, ionic, as well as hydrogen- and van der Waals-bonded systems alike. In this work, we focus on assessing the performance of the SCAN functional for itinerant magnets by calculating basic structural and magnetic properties of the transition metals Fe, Co, and Ni. We find that although structural properties of bcc-Fe seem to be in good agreement with experiment, SCAN performs worse than standard local and semilocal functionals for fcc-Ni and hcp-Co. In all three cases, the magnetic moment is significantly overestimated by SCAN, and the 3d states are shifted to lower energies, as compared to experiments.

  • 281.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Larsson, Petter
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Helmersson, Ulf
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni1-xMn1+xSb2010Ingår i: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979, Vol. 108, nr 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We perform a combined theoretical and experimental study of the phase stability and magnetism of the off-stoichiometric Ni1-xMn1+xSb in the half-Heusler crystal phase. Our work is motivated by the need for strategies to engineer the magnetism of potentially half-metallic materials, such as NiMnSb, for improved performance at elevated temperatures. By means of ab initio calculations we investigate Ni1-xMn1+xSb over the whole composition range 0 andlt;= x andlt;= 1 of Ni replacing Mn and show that at relevant temperatures, the half-Heusler phase should be thermodynamically stable up to at least x=0.20 with respect to the competing C38 structure of Mn2Sb. Furthermore we find that half-Heusler Ni1-xMn1+xSb retains half-metallic band structure over the whole concentration range and that the magnetic moments of substitutional Mn-Ni atoms display magnetic exchange interactions an order of magnitude larger than the Ni-Mn interaction in NiMnSb. We also demonstrate experimentally that the alloys indeed can be created by synthesizing off-stoichiometric Ni1-xMn1+xSb films on MgO substrates by means of magnetron sputtering.

  • 282.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Mikhaylushkin, Arkady
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Johansson, B
    Royal Institute Technology KTH.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Configurational thermodynamics of Fe-Ni alloys at Earths core conditions2011Ingår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 308, nr 1-2, s. 90-96Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By means of ab-initio calculations, we perform an analysis of the configurational thermodynamics, effects of disorder, and structural energy differences in Fe-Ni alloys at the pressure and temperature conditions of the Earths core. We show from ab-initio calculations that the ordering energies of fcc and hcp-structured Fe-Ni solid solutions at these conditions depend sensitively on the alloy configuration, i.e., on the degree of chemical disorder, and are on a scale comparable with the structural energy differences. From configurational thermodynamic simulations we find that a distribution of Fe and Ni atoms in the solutions should be very close to completely disordered at these conditions. Using this model of the Fe-Ni system, we have calculated the fcc-hcp structural free energy difference in a wide pressure-temperature range of 120-360 GPa and 1000-6600K. Our calculations show that alloying of Fe with Ni below 3000 K favours stabilisation of the fcc phase over the hcp, in agreement with experiments. However, above 3000 K the effect is reversed, and at conditions corresponding to those of the Earths inner core, Ni acts as an agent to stabilise the hcp phase.

  • 283.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Bayreuth, Germany.
    Schoenleber, A.
    Univ Bayreuth, Germany.
    van Smaalen, S.
    Univ Bayreuth, Germany.
    The role of magnetic order in VOCl2019Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, nr 32, artikel-id 325502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    VOCl and other transition metal oxychlorides are candidate materials for next-generation rechargeable batteries. We have investigated the influence of the underlying magnetic order on the crystallographic and electronic structure by means of density functional theory. Our study shows that antiferromagnetic ordering explains the observed low-temperature monoclinic distortion of the lattice, which leads to a decreased distance between antiferromagnetically coupled V-V nearest neighbors. We also show that the existence of a local magnetic moment removes the previously suggested degeneracy of the occupied levels, in agreement with experiments. To describe the electronic structure, it turns out crucial to take the correct magnetic ordering into account, especially at elevated temperature.

  • 284.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Supercell Calculations of Hyperfine Interactions in Transition-Metal AlloysManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We have performed calculations for the hyperfine field in the disordered Fe0.5Ni0.5 alloy using supercells with up to 864 atoms. The computational scheme is based on exact muffin-tin orbitals and the locally self-consistent Green’s function formalism, which scales linearly with the number of atoms in the supercell. This scheme allows local environment effects, such as chemical and magnetic environment, and short-range order, to be explicitly included. Supercell calculations for Fe-Ni show that while the average fields coincides with that obtained using the coherent potential approximation, there is a significant distribution of the hyperfine fields depending on the local environment. The fields of Fe and Ni show qualitatively different behaviour as a function of the on-site magnetic moment, but scale linearly with the average magnetic moment in the first coordination shell.

  • 285.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Zapolsky, H
    University of Rouen.
    Ruban, A V
    Royal Institute of Technology.
    Vernyhora, I
    University of Rouen.
    Ledue, D
    University of Rouen.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Influence of the Magnetic State on the Chemical Order-Disorder Transition Temperature in Fe-Ni Permalloy2010Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 16, s. 167208-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 286.
    Eklof, Daniel
    et al.
    Stockholm Univ, Sweden.
    Fischer, Andreas
    Augsburg Univ, Germany.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Commiss Higher Educ, Thailand.
    Jaworski, Aleksander
    Stockholm Univ, Sweden.
    Pell, Andrew J.
    Stockholm Univ, Sweden.
    Grins, Jekabs
    Stockholm Univ, Sweden.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Wu, Yang
    Tsinghua Univ, Peoples R China.
    Widom, Michael
    Carnegie Mellon Univ, PA 15213 USA.
    Scherer, Wolfgang
    Augsburg Univ, Germany.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Mysterious SiB3: Identifying the Relation between alpha- and beta-SiB32019Ingår i: ACS OMEGA, ISSN 2470-1343, Vol. 4, nr 20, s. 18741-18759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Binary silicon boride SiB3 has been reported to occur in two forms, as disordered and nonstoichiometric alpha-SiB3-x, which relates to the alpha-rhombohedral phase of boron, and as strictly ordered and stoichiometric beta-SiB3. Similar to other boron-rich icosahedral solids, these SiB3 phases represent potentially interesting refractory materials. However, their thermal stability, formation conditions, and thermodynamic relation are poorly understood. Here, we map the formation conditions of alpha-SiB3-x and beta-SiB3 and analyze their relative thermodynamic stabilities. alpha-SiB3-x is metastable (with respect to beta-SiB3 and Si), and its formation is kinetically driven. Pure polycrystalline bulk samples may be obtained within hours when heating stoichiometric mixtures of elemental silicon and boron at temperatures 1200-1300 degrees C. At the same time, alpha-SiB3-x decomposes into SiB6 and Si, and optimum time-temperature synthesis conditions represent a trade-off between rates of formation and decomposition. The formation of stable beta-SiB3 was observed after prolonged treatment (days to weeks) of elemental mixtures with ratios Si/B = 1:11:4 at temperatures 1175-1200 degrees C. The application of high pressures greatly improves the kinetics of SiB3 formation and allows decoupling of SiB3 formation from decomposition. Quantitative formation of beta-SiB3 was seen at 1100 degrees C for samples pressurized to 5.5-8 GPa. beta-SiB3 decomposes peritectoidally at temperatures between 1250 and 1300 degrees C. The highly ordered nature of beta-SiB3 is reflected in its Raman spectrum, which features narrow and distinct lines. In contrast, the Raman spectrum of alpha-SiB3-x is characterized by broad bands, which show a clear relation to the vibrational modes of isostructural, ordered B6P. The detailed composition and structural properties of disordered alpha-SiB3-x were ascertained by a combination of single-crystal X-ray diffraction and Si-29 magic angle spinning NMR experiments. Notably, the compositions of polycrystalline bulk samples (obtained at T amp;lt;= 1200 degrees C) and single crystal samples (obtained from Si-rich molten Si-B mixtures at T amp;gt; 1400 degrees C) are different, SiB2.93(7) and SiB2.64(2), respectively. The incorporation of Si in the polar position of B-12 icosahedra results in highly strained cluster units. This disorder feature was accounted for in the refined crystal structure model by splitting the polar position into three sites. The electron-precise composition of alpha-SiB3-x is SiB2.5 and corresponds to the incorporation of, on average, two Si atoms in each B-12 icosahedron. Accordingly, alpha-SiB3-x constitutes a mixture of B10Si2 and B11Si clusters. The structural and phase stability of alpha-SiB3-x were explored using a first-principles cluster expansion. The most stable composition at 0 K is SiB2.5, which however is unstable with respect to the decomposition beta-SiB3 + Si. Modeling of the configurational and vibrational entropies suggests that alpha-SiB3-x only becomes more stable than beta-SiB3 at temperatures above its decomposition into SiB6 and Si. Hence, we conclude that alpha-SiB3-x is metastable at all temperatures. Density functional theory electronic structure calculations yield band gaps of similar size for electron-precise alpha-SiB2.5 and beta-SiB3, whereas alpha-SiB3 represents a p-type conductor.

  • 287.
    Eklöf, Anna
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Kaneryd, Linda
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Climate change in metacommunities: dispersal gives double-sided effects on persistence2012Ingår i: Philosphical Transactions of the Royal Society B, ISSN 1471-2970, Vol. 367, nr 1605, s. 2945-2954Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is increasingly affecting the structure and dynamics of ecological communities bothat local and at regional scales, and this can be expected to have important consequences for theirrobustness and long-term persistence. The aim of the present work is to analyse how the spatialstructure of the landscape and dispersal patterns of species (dispersal rate and average dispersal distance)affects metacommunity response to two disturbances: (i) increased mortality during dispersaland (ii) local species extinction. We analyse the disturbances both in isolation and in combination.Using a spatially and dynamically explicit metacommunity model, we find that the effect of dispersalon metacommunity persistence is two-sided: on the one hand, high dispersal significantly reducesthe risk of bottom-up extinction cascades following the local removal of a species; on the otherhand, when dispersal imposes a risk to the dispersing individuals, high dispersal increases extinctionrisks, especially when dispersal is global. Large-bodied species with long generation times at thehighest trophic level are particularly vulnerable to extinction when dispersal involves a risk. Thissuggests that decreasing the mortality risk of dispersing individuals by improving the quality ofthe habitat matrix may greatly increase the robustness of metacommunities.

  • 288.
    Eklöf, Anna
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Ebenman, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Effects of dispersal on local extinctions in multi-trophic metacommunitiesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    As a result of habitat destruction many ecological communities have a fragmented distribution and are built up of partially isolated local communities connected through dispersal of interacting species. The dynamics of such metacommunities is governed both by local processes (interactions among species coexisting within habitat patches) and regional processes (movement of species among habitat patches). Earlier theoretical work on simple metacommunities have mainly focused on the positive effects of space and dispersal for the coexistence of interacting species and hence for local and regional species diversity. However, it is plausible that dispersal might also pose some kind of risk to the dispersing individuals. Here we explore how such risks might affect the dynamics of metacommunities. We develop spatially and dynamically explicit models to investigate how the trophic structure (connectance) of local communities, the spatial structure of the metacommunity and the dispersal characteristics of species affect species extinction risks. Species extinction risks in these open communities are measured relative to the extinction risks in closed communities (i.e. no dispersal). We show that the introduction of dispersal among initially closed local communities might lead to increased probability of local species extinction. The effects of dispersal depend on migration rate, movement pattern of individuals and the density of patches in the landscape. Specifically, when dispersal involves a risk, high migration rates, global dispersal and low patch density will all lead to increased probability of local species extinctions. Furthermore, the trophic structure of local communities plays a significant role in the response of metacommunities to changes in the regional processes.

  • 289.
    Eklöf, Anna
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Kaneryd, Linda
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Ebenman, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Biologi. Linköpings universitet, Tekniska högskolan.
    Can dispersal rescue metacommunities from extinction cascades?Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Climate change and habitat loss are increasingly affecting the structure and dynamics of ecological communities both at the local and regional scale. Changes in the spatial structure of landscapes as well as in the trophic structure of local communities can be expected to have important consequences for the long-term persistence of species in metacommunities. The aim of the present work is to investigate how the spatial structure of the landscape (patch density) and dispersal patterns of species (migration rate and dispersal distance) affect a metacommunities response to local loss of species and to increased mortality of individuals during dispersal. Using a spatially and dynamically explicit metacommunity model we find that the effect of dispersal on metacommunity persistence is two-sided: on the one hand, when dispersal involves no risk, high migration rate significantly reduces the risk of bottom-up extinction cascades following the local removal of a species. The explanation for this is that recolonization rates of the locally removed species increases with increasing migration rate. On the other hand, when dispersal imposes a risk to the dispersing individuals, high migration rate increases extinction risks, especially when dispersal is global (long dispersal distances). Largebodied species with long generation times at the highest trophic level are particularly vulnerable to extinction when dispersal involves a risk. These results suggest that decreasing the mortality risk of dispersing individuals by improving the quality of the habitat matrix might greatly increase the robustness of metacommunities to local loss of species by enhancing recolonizations and rescue effects.

  • 290.
    Ektarawong, Annop
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Thermodynamic consideration and ground-state search of icosahedral boron subselenide B-12(B1-xSex)(2) from a first-principles cluster expansion2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 17, artikel-id 174103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phase stability of icosahedral boron subselenide B-12(B1-xSex)(2), where 0.5 amp;lt;= x amp;lt;= 1, is explored using a first-principles cluster expansion. The results shows that, instead of a continuous solid solution, B-12(B1-xSex)(2) is thermodynamically stable as an individual line compound at the composition of B9.5Se. The ground-state configuration of B9.5Se is represented by a mixture of B-12(Se-Se), B-12(B-Se), and B-12(Se-B) with a ratio of 1: 1: 1, where they form a periodic ABCABC... stacking sequence of B-12(Se-Se), B-12(B-Se), and B-12(Se-B) layers along the c axis of the hexagonal conventional unit cell. The structural and electronic properties of the ground-state B9.5Se are also derived and discussed. By comparing the derived ground-state properties of B9.5Se to the existing experimental data of boron subselenide B similar to 13Se, I proposed that the as-synthesized boron subselenide B similar to 13Se, as reported in the literature, has the actual composition of B9.5Se.

  • 291.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Max Planck Inst Eisenforsch GmbH, Germany.
    Stability of SnSe1-xSx solid solutions revealed by first-principles cluster expansion2018Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, nr 29, artikel-id 29LT01Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The configurational thermodynamics of a pseudo-binary alloy SnSe1-xSx in the Pnma phase is studied using first-principles cluster-expansion method in combination with canonical Monte Carlo simulations. We find that, despite the alloy having a tendency toward a phase decomposition into SnSe and SnS at 0 K, the two constituent binaries readily mix with each other to form random SnSe1-xSx solid solutions even at a temperature below room temperature. The obtained isostructural phase diagram of SnSe1-xSx reveals that the alloy is thermodynamically stable as a single-phase random solid solution over a whole composition range above 200 K. These findings provide a fundamental understanding on the alloying behavior of SnSe1-xSx and bring clarity to the debated clustering tendency in this alloy system.

  • 292.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Chulalongkorn Univ, Thailand; Natl Univ Singapore, Singapore; Natl Univ Singapore, Singapore; Thailand Ctr Excellence Phys, Thailand.
    Feng, Y. P.
    Natl Univ Singapore, Singapore.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Phase stability of two-dimensional monolayer As1-xPx solid solutions revealed by a first-principles cluster expansion2019Ingår i: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, nr 5, artikel-id 054005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phase stability of two-dimensional monolayer As1-xPx solid solutions, exhibiting the puckered (alpha phase) and buckled (beta phase) structures are investigated using a first-principles cluster-expansion method. Canonical Monte Carlo simulations, together with harmonic approximation, are performed to capture the influences of thermally induced configurational disorder and lattice vibrations on the phase stability of monolayer As1-xPx. We first demonstrate that, as the temperature approaches 0 K, the monolayer As1-xPx displays a tendency toward phase separation into its constituent elemental phases, and thus no stable ordered structures of As1-xPx, both alpha and beta phases, are predicted to be thermodynamically stable. We further reveal with the inclusion of the lattice vibrational contributions that beta-As1-xPx is thermodynamically favored over alpha-As1-xPx, across the entire composition range even at 0 K and increasingly so at higher temperature, and a continuous series of disordered solid solution of beta-As1-xPx, where 0 amp;lt;= x amp;lt;= 1, is predicted at the temperature above 550 K. These findings not only indicate that the ordered structures of monolayer alpha-As1-xPx, and beta-As1-xPx, frequently studied in the literature, may not exist in nature, but also presumably suggest that monolayer alpha-As1-xPx is metastable with respect to monolayer beta-As1-xPx.

  • 293.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Singapore, Singapore.
    Peng, Y. P.
    Natl Univ Singapore, Singapore.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Phase stability of three-dimensional bulk and two-dimensional monolayer As1-xSbx solid solutions from first principles2019Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, nr 24, artikel-id 245702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mixing thermodynamics of both three-dimensional bulk and two-dimensional monolayered alloys of As1-xSbx as a function of alloy composition and temperature are explored using a first-principles cluster-expansion method, combined with canonical Monte-Carlo simulations. We observe that, for the bulk phase, As1-xSbx alloy can exhibit not only chemical ordering of As and Sb atoms at x = 0.5 to form an ordered compound of AsSb stable upon annealing up to T approximate to 475 K, but also a miscibility gap at 475 K less than or similar to T less than or similar to 550 K in which two disordered solid solutions of As1-xSbx of different alloy compositions thermodynamically coexist. At T amp;gt; 550 K, a single-phase solid solution of bulk As1-xSbx is predicted to be stable across the entire composition range. These results clearly explain the existing uncertainties in the alloying behavior of bulk As1-xSbx alloy, as previously reported in the literature, and also found to be in qualitative and quantitative agreement with the experimental observations. Interestingly, the alloying behavior of As1-xSbx is considerably altered, as the dimensionality of the material reduces from the three-dimensional bulk state to the two-dimensional monolayered state-for example, a single-phase solid solution of monolayer As1-xSbx is predicted to be stable over the whole composition range at T amp;gt; 250 K. This distinctly highlights an influence of the reduced dimensionality on the alloying behavior of As1-xSbx.

  • 294.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Max Planck Institute Eisenforsch GmbH, Germany.
    Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles2016Ingår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, nr 5, artikel-id 054104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B4C to B2C, using first-principles calculations. Apart fromB4C, generally addressed in the literature, B2.5C, represented by B10C2p (C-C), where C-p and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B4C as well as pure boron and carbon phases. The thermodynamic stability of B2.5C is determined by the Gibbs free energy G as a function of pressure p and temperature T, in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B2.5C is then illustrated through the p-T phase diagrams. Depending on the temperatures, the stability range of B2.5C is predicted to be within the range between 40 and 67 GPa. At T greater than or similar to 500 K, the icosahedral C-p atoms in B2.5C configurationally disorder at the polar sites. By investigating the properties of B2.5C, e.g., elastic constants and phonon and electronic density of states, we demonstrate that B2.5C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B2.5C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

  • 295.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Max Planck Inst Eisenforsch GmbH, Germany.
    Effect of temperature and configurational disorder on the electronic band gap of boron carbide from first principles2018Ingår i: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, nr 10, artikel-id 104603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The overestimation, rather than the usual underestimation, of the electronic band gap at 0 K of boron carbide with the ideally stoichiometric composition of B4C, represented by B11CP (CBC), in density functional theory calculations is one of the outstanding controversial issues in the field of icosahedral boron-rich solids. Using a first-principles approach, we explore the effect of temperature and configurational disorder on the electronic band gap of B4C. Ab initio molecular dynamics simulations are performed to account for the effects of vibrational disorder. The results reveal that the volumetric thermal expansion as well as the thermally induced configurational disorder of icosahedral C-P atoms residing in the B11CP icosahedra have a minimal impact on the band gap of B4C, while a major decrease of the band gap is caused by explicit atomic displacements, induced by lattice vibrations. At 298 K, the band gap of B4C is overestimated, as compared to the experimental value, by approximately 31%. However, configurational disorder induced by introducing a small fraction of B-12 (CBC) and B-12 (B-4) into a matrix of B11CP (CBC) to make the composition of boron carbide approximately B4.3C, claimed to be the carbon-rich limit of the material in experiment, leads to a smaller band gap due to the appearance of midgap states. These results can explain at least a part of the previous discrepancies between theory and experiments for the band gap of boron carbide.

  • 296.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Max Planck Institute Eisenforsch GmbH, Germany.
    First-principles prediction of stabilities and instabilities of compounds and alloys in the ternary B-As-P system2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 2, artikel-id 024202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We examine the thermodynamic stability of compounds and alloys in the ternary B-As-P system theoretically using first-principles calculations. We demonstrate that the icosahedral B12As2 is the only stable compound in the binary B-As system, while the zinc-blende BAs is thermodynamically unstable with respect to B12As2 and the pure arsenic phase at 0 K, and increasingly so at higher temperature, suggesting that BAs may merely exist as a metastable phase. On the contrary, in the binary B-P system, both zinc-blende BP and icosahedral B12P2 are predicted to be stable. As for the binary As-P system, As1-xPx disordered alloys are predicted at elevated temperature-for example, a disordered solid solution of up to similar to 75 at.% As in black phosphorus as well as a small solubility of similar to 1 at.% P in gray arsenic at T = 750 K, together with the presence of miscibility gaps. The calculated large solubility of As in black phosphorus explains the experimental syntheses of black-phosphorus-type As1-xPx alloys with tunable compositions, recently reported in the literature. We investigate the phase stabilities in the ternary B-As-P system and demonstrate a high tendency for a formation of alloys in the icosahedral B-12(As1-xPx)(2) structure by intermixing of As and P atoms at the diatomic chain sites. The phase diagram displays noticeable mutual solubility of the icosahedral subpnictides in each other even at room temperature as well as a closure of a pseudobinary miscibility gap around 900 K. As for pseudobinary BAs1-xPx alloys, only a tiny amount of BAs is predicted to be able to dissolve in BP to form the BAs1-xPx disordered alloys at elevated temperature. For example, less than 5% of BAs can dissolve in BP at T = 1000 K. The small solubility limit of BAs in BP is attributed to the thermodynamic instability of BAs with respect to B12As2 and As.

  • 297.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Max Planck Inst Eisenforsch GmbH, Germany.
    Structural models of increasing complexity for icosahedral boron carbide with compositions throughout the single-phase region from first principles2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 17, artikel-id 174104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We perform first-principles calculations to investigate the phase stability of boron carbide, concentrating on the recently proposed alternative structural models composed not only of the regularly studied B11Cp(CBC) and B-12(CBC), but also of B-12(CBCB) and B-12(B-4). We find that a combination of the four structural motifs can result in low-energy electron precise configurations of boron carbide. Among several considered configurations within the composition range of B10.5C and B4C, we identify in addition to the regularly studied B11Cp(CBC) at the composition of B4C two low-energy configurations, resulting in a new view of the B-C convex hull. Those are [B-12(CBC)](0.67)[B-12(B-4)](0.33) and [B-12(CBC)](0.67)[B-12(CBCB)](0.33), corresponding to compositions of B10.5C and B6.67C, respectively. As a consequence, B-12(CBC) at the composition of B6.5C, previously suggested in the literature as a stable configuration of boron carbide, is no longer part of the B-C convex hull. By inspecting the electronic density of states as well as the elastic moduli, we find that the alternative models of boron carbide can provide a reasonably good description for electronic and elastic properties of the material in comparison with the experiments, highlighting the importance of considering B-12(CBCB) and B-12(B-4), together with the previously proposed B11Cp(CBC) and B-12(CBC), as the crucial ingredients for modeling boron carbide with compositions throughout the single-phase region.

  • 298.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Max Planck Institute Eisenforsch GmbH, Germany.
    Thermodynamic stability and properties of boron subnitrides from first principles2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 6, artikel-id 064206Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    We use the first-principles approach to clarify the thermodynamic stability as a function of pressure and temperature of three different alpha-rhombohedral-boron-like boron subnitrides, with the compositions of B6N, B13N2, and B38N6, proposed in the literature. We find that, out of these subnitrides with the structural units of B-12(N-N), B-12(NBN), and [B-12(N-N)](0.33)[B-12(NBN)](0.67), respectively, only B38N6, represented by [B-12(N-N)](0.33)[B-12(NBN)](0.67), is thermodynamically stable. Beyond a pressure of about 7.5 GPa depending on the temperature, also B38N6 becomes unstable, and decomposes into cubic boron nitride and a-tetragonalboron- like boron subnitride B50N2. The thermodynamic stability of boron subnitrides and relevant competing phases is determined by the Gibbs free energy, in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. We calculate lattice parameters, elastic constants, phonon and electronic density of states, and demonstrate that [B-12(N-N)](0.33)[B-12(NBN)](0.67) is bothmechanically and dynamically stable, and is an electrical semiconductor. The simulated x-ray powder-diffraction pattern as well as the calculated lattice parameters of [B-12(N-N)](0.33)[B-12(NBN)](0.67) are found to be in good agreement with those of the experimentally synthesized boron subnitrides reported in the literature, verifying that B38N6 is the stable composition of a-rhombohedral-boron-like boron subnitride.

  • 299.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Max Planck Institute Eisenforsch GmbH, Germany.
    Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 1, artikel-id 014202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to a large discrepancy between theory and experiment, the electronic character of crystalline boron carbide B13C2 has been a controversial topic in the field of icosahedral boron-rich solids. We demonstrate that this discrepancy is removed when configurational disorder is accurately considered in the theoretical calculations. We find that while the ordered ground state B13C2 is metallic, the configurationally disordered B13C2, modeled with a superatom-special quasirandom structure method, goes through a metal to nonmetal transition as the degree of disorder is increased with increasing temperature. Specifically, one of the chain-end carbon atoms in the CBC chains substitutes a neighboring equatorial boron atom in a B-12 icosahedron bonded to it, giving rise to a B11Ce(BBC) unit. The atomic configuration of the substitutionally disordered B13C2 thus tends to be dominated by a mixture between B-12(CBC) and B11Ce(BBC). Due to splitting of valence states in B11Ce(BBC), the electron deficiency in B-12(CBC) is gradually compensated.

  • 300.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 2, artikel-id 024204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Configurationally disordered crystalline boron carbide, with the composition B4C, is studied using first-principles calculations. We investigate both dilute and high concentrations of carbon-boron substitutional defects. For the latter purpose, we suggest a superatoms picture of the complex structure and combine it with a special quasirandom structure approach for disorder. In this way, we model a random distribution of high concentrations of the identified low-energy defects: (1) bipolar defects and (2) rotation of icosahedral carbon among the three polar-up sites. Additionally, the substitutional disorder of the icosahedral carbon at all six polar sites, as previously discussed in the literature, is also considered. Two configurational phase transitions from the ordered to the disordered configurations are predicted to take place upon an increase in temperature using a mean-field approximation for the entropy. The first transition, at 870 K, induces substitutional disorder of the icosahedral carbon atoms among the three polar-up sites; meanwhile the second transition, at 2325 K, reveals the random substitution of the icosahedral carbon atoms at all six polar sites coexisting with bipolar defects. Already the first transition removes the monoclinic distortion existing in the ordered ground-state configuration and restore the rhombohedral system (R3m). The restoration of inversion symmetry yielding the full rhombohedral symmetry (R (3) over barm) on average, corresponding to what is reported in the literature, is achieved after the second transition. Investigating the effects of high pressure on the configurational stability of the disordered B4C phases reveals a tendency to stabilize the ordered ground-state configuration as the configurationally ordering/disordering transition temperature increases with pressure exerted on B4C. The electronic density of states, obtained from the disordered phases, indicates a sensitivity of the band gap to the degree of configurational disorder in B4C.

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