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  • 101.
    Skripnyak, Vladimir A.
    et al.
    Natl Res Tomsk State Univ, Russia.
    Skripnyak, Vladimir V.
    Natl Res Tomsk State Univ, Russia.
    Skripnyak, Evgeniya G.
    Natl Res Tomsk State Univ, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Res Tomsk State Univ, Russia.
    MODELLING OF THE MECHANICAL RESPONSE OF Zr-Nb AND Ti-Nb ALLOYS IN A WIDE TEMPERATURE RANGE2018In: IRF2018: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON INTEGRITY-RELIABILITY-FAILURE, INEGI-INST ENGENHARIA MECANICA E GESTAO INDUSTRIAL , 2018, p. 855-862Conference paper (Refereed)
    Abstract [en]

    This article presents the results of modelling of the mechanical behaviour of biocompatible Zr-Nb and Ti-Nb alloys in the range of strain rates from 10(-3) to 10(3) s(-1) at temperatures from 297 K to 1273 K. Modification of the micro-dynamical model was proposed for the description of Zr-1Nb ultrafine grained and coarse grained alloys. It was shown that the phase transition HCP -amp;gt; BCC alloy Zr-Nb at elevated temperatures leads to a sharp changing in the resistance to plastic flow and kinetics of growth of damage. The results can be used for engineering analysis of designed constructive elements of technical and biomedical applications.

  • 102.
    Karlsson, H.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Yakymenko, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nature of magnetization and lateral spin-orbit interaction in gated semiconductor nanowires2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 21, article id 215302Article in journal (Refereed)
    Abstract [en]

    Semiconductor nanowires are interesting candidates for realization of spintronics devices. In this paper we study electronic states and effects of lateral spin-orbit coupling (LSOC) in a one-dimensional asymmetrically biased nanowire using the Hartree-Fock method with Dirac interaction. We have shown that spin polarization can be triggered by LSOC at finite source-drain bias,as a result of numerical noise representing a random magnetic field due to wiring or a random background magnetic field by Earth magnetic field, for instance. The electrons spontaneously arrange into spin rows in the wire due to electron interactions leading to a finite spin polarization. The direction of polarization is, however, random at zero source-drain bias. We have found that LSOC has an effect on orientation of spin rows only in the case when source-drain bias is applied.

  • 103.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nature of the octahedral tilting phase transitions in perovskites: A case study of CaMnO32018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 2, article id 024108Article in journal (Refereed)
    Abstract [en]

    The temperature-induced antiferrodistortive (AFD) structural phase transitions in CaMnO3, a typical perovskite oxide, are studied using first-principles density functional theory calculations. These transitions are caused by tilting of the MnO6 octahedra that are related to unstable phonon modes in the high-symmetry cubic perovskite phase. Transitions due to octahedral tilting in perovskites normally are believed to fit into the standard soft-mode picture of displacive phase transitions. We calculate phonon-dispersion relations and potential-energy landscapes as functions of the unstable phonon modes and argue based on the results that the phase transitions are better described as being of order-disorder type. This means that the cubic phase emerges as a dynamical average when the system hops between local minima on the potential-energy surface. We then perform ab initio molecular dynamics simulations and find explicit evidence of the order-disorder dynamics in the system. Our conclusions are expected to be valid for other perovskite oxides, and we finally suggest how to predict the nature (displacive or order-disorder) of the AFD phase transitions in any perovskite system.

  • 104.
    Rivera Vila, Henrique Vieira
    et al.
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Machado de Macedo, Luiz Guilherme
    Fed Univ Para, Brazil.
    Gargano, Ricardo
    Univ Brasilia, Brazil.
    On the Angular Distribution of the H+Li-2 Cross Sections: a Converged Time-Independent Quantum Scattering Study2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 1044Article in journal (Refereed)
    Abstract [en]

    A thorough time-independent quantum scattering study is performed on a benchmark potential energy surface for the H+Li-2 reaction at the fundamental electronic state. Integral and differential cross sections are calculated along with thermal rate coefficients until convergence is reached. Our findings show that vibrational and rotational excitations of the reactant hinder reactivity, though for the latter a considerable reaction promotion was spotted as we increase the reactant rotational quantum number until the critical value of j = 4. Such a promotion then begins to retract, eventually becoming an actual inhibition for larger j. In a straightforward manner, the concept of time-independent methods implemented in this study allowed this accurate state-to-state analysis. Furthermore, a nearly isotropic behaviour of the scattering is noted to take place from the angular point of view. Remarkably, our computational protocol is ideally suited to yield converged thermal rate coefficients, revealing a non-Arrhenius pattern and showing that J-shifting approach fails to describe this particular reaction. Our results, when compared to previous and independent ones, reinforce the latest theoretical reference for future validation in the experimental field.

  • 105.
    Garhammer, Julian
    et al.
    Univ Bayreuth, Germany.
    Hofmann, Fabian
    Univ Bayreuth, Germany.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Kuemmel, Stephan
    Univ Bayreuth, Germany.
    On the challenge to improve the density response with unusual gradient approximations2018In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 91, no 7, article id 159Article in journal (Refereed)
    Abstract [en]

    Certain excitations, especially ones of long-range charge transfer character, are poorly described by time-dependent density functional theory (TDDFT) when typical (semi-)local functionals are used. A proper description of these excitations would require an exchange-correlation response differing substantially from the usual (semi-) local one. It has recently been shown that functionals of the generalized gradient approximation (GGA) type can yield unusual potentials, mimicking features of the exact exchange derivative discontinuity and showing divergences on orbital nodal surfaces. We here investigate whether these unusual potential properties translate into beneficial response properties. Using the Sternheimer formalism we closely investigate the response obtained with the 2013 exchange approximation by Armiento and Kummel (AK13) and the 1988 exchange approximation by Becke (B88), both of which show divergences on orbital nodal planes. Numerical calculations for Na-2 as well as analytical and numerical calculations for the hydrogen atom show that the response of AK13 behaves qualitatively different from usual semi-local functionals. However, the AK13 functional leads to fundamental instabilities in the asymptotic region that prevent its practical application in TDDFT. Our findings may help the development of future improved functionals. They also corroborate that the frequency-dependent Sternheimer formalism is excellently suited for running and analyzing TDDFT calculations.

  • 106.
    Lischka, Matthias
    et al.
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Fritton, Massimo
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Eichhorn, Johanna
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Vyas, Vijay S.
    Max Planck Inst Solid State Res, Germany; Marquette Univ, WI 53233 USA.
    Strunskus, Thomas
    Christian Albrechts Univ Kiel, Germany.
    Lotsch, Bettina V.
    Max Planck Inst Solid State Res, Germany; Nanosyst Initiat Munich, Germany; Ctr NanoSci, Germany; Univ Munich LMU, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Heckl, Wolfgang M.
    Tech Univ Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Ctr NanoSci, Germany.
    Lackinger, Markus
    Tech Univ Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Ctr NanoSci, Germany.
    On-Surface Polymerization of 1,6-Dibromo-3,8-diiodpyrene-A Comparative Study on Au(111) Versus Ag(111) by STM, XPS, and NEXAFS2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 11, p. 5967-5977Article in journal (Refereed)
    Abstract [en]

    The surface chemistry of 1,6-dibromo-3,8-diiodopyrene (Br2I2Py) is comparatively studied on Au(111) versus Ag(111) surfaces under ultrahigh vacuum conditions by a combination of high-resolution scanning tunneling microscopy (STM) and X-ray spectroscopy. The chemical state of the molecular networks, that is, the dehalogenation and the possible formation of organometallic intermediates, is assessed by X-ray photoelectron spectroscopy. In addition, pyrene tilt angles are quantified by carbon K-edge near edge X-ray absorption fine structure experiments. Upon room-temperature (RT) deposition of Br2I2Py onto Au(111), only partial deiodination was found, and STM revealed the coexistence of ordered arrangements of both intact Br2I2Py molecules and organometallic dimers as well as few larger aggregates. Further annealing to 100 C triggered full deiodination followed by the formation of organometallic chains of otherwise still brominated molecules. By contrast, on Ag(111), iodine is fully and bromine is partly dissociated upon RT deposition of Br2I2Py. The initially disordered organometallic aggregates can be reorganized into more ordered structures by mild annealing at 125 degrees C. Yet, the conversion of the organometallic intermediates into well-defined cross-linked quasi 2D covalent networks was neither possible on Au(111) nor on Ag(111). This is attributed to the large steric hindrance in the covalently linked adsorbed state.

  • 107.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Phase Stability of Dynamically Disordered Solids from First Principles2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 22, article id 225702Article in journal (Refereed)
    Abstract [en]

    Theoretical studies of phase stability in solid materials with dynamic disorder are challenging due to the failure of the standard picture of atoms vibrating around fixed equilibrium positions. Dynamically disordered solid materials show immense potential in applications. In particular, superionic conductors, where the disorder results in exceptionally high ionic conductivity, are very promising as solid state electrolytes in batteries and fuel cells. The biggest obstacle in living up to this potential is the limited stability of the dynamically disordered phases. Here, we outline a method to obtain the free energy of a dynamically disordered solid. It is based on a stress-strain thermodynamic integration on a deformation path between a mechanically stable ordered variant of the disordered phase, and the dynamically disordered phase itself. We show that the large entropy contribution associated with the dynamic disorder is captured in the behavior of the stress along the deformation path. We apply the method to Bi2O3, whose superionic delta phase is the fastest known solid oxide ion conductor. We accurately reproduce the experimental transition enthalpy and the critical temperature of the phase transition from the low temperature ground state a phase to the superionic d phase. The method can be used for a first-principles description of the phase stability of superionic conductors and other materials with dynamic disorder, when the disordered phase can be connected to a stable phase through a continuous deformation path.

  • 108.
    Herriman, Jane E.
    et al.
    CALTECH, CA 91125 USA.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. CALTECH, CA 91125 USA.
    Fultz, Brent
    CALTECH, CA 91125 USA.
    Phonon thermodynamics and elastic behavior of GaN at high temperatures and pressures2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 21, article id 214105Article in journal (Refereed)
    Abstract [en]

    The effects of temperature and pressure on the phonons of GaN were calculated for both the wurtzite and zinc-blende structures. The quasiharmonic approximation (QHA) gave reasonable results for the temperature dependence of the phonon DOS at zero pressure but unreliably predicted the combined effects of temperature and pressure. Pressure was found to change the explicit anharmonicity, altering the thermal shifts of phonons and more notably qualitatively changing the evolution of phonon lifetimes with increasing temperature. These effects were largest for the optical modes, and phonon frequencies below approximately 5 THz were adequately predicted with the QHA. The elastic anisotropies of GaN in both wurtzite and zinc-blende structures were calculated from the elastic constants as a function of pressure at 0 K. The elastic anisotropy increased with pressure until reaching elastic instabilities at 40 GPa (zinc blende) and 65 GPa (wurtzite). The calculated instabilities are consistent with proposed transformation pathways to rocksalt GaN and place upper bounds on the pressures at which wurtzite and zinc-blende GaN can be metastable.

  • 109.
    Greenberg, Eran
    et al.
    Tel Aviv Univ, Israel; Univ Chicago, IL 60637 USA.
    Leonov, Ivan
    Inst Met Phys, Russia; NUST MISIS, Russia.
    Layek, Samar
    Tel Aviv Univ, Israel.
    Konopkova, Zuzana
    PETRA III, Germany.
    Pasternak, Moshe P.
    Tel Aviv Univ, Israel.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Jeanloz, Raymond
    Univ Calif Berkeley, CA 94720 USA.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Rozenberg, Gregory Kh.
    Tel Aviv Univ, Israel.
    Pressure-Induced Site-Selective Mott Insulator-Metal Transition in Fe2O32018In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 8, no 3, article id 031059Article in journal (Refereed)
    Abstract [en]

    We provide experimental and theoretical evidence for a pressure-induced Mott insulator-metal transition in Fe2O3 characterized by site-selective delocalization of the electrons. Density functional plus dynamical mean field theory (DFT + DMFT) calculations, along with Mossbauer spectroscopy, x-ray diffraction, and electrical transport measurements on Fe2O3 up to 100 GPa, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by ((FE3+HS)-F-VI)(2)O-3 [R (3) over barc structure]-amp;gt;(50) (GPa) (Fe-VIII(3+HS) Fe-VI(M))O-3 [P2(1)/n structure]-amp;gt;(68 Gpa)(Fe-VI(M))(2)O-3[Aba2/PPv structure]. Within the P2(1)/n crystal structure, characterized by two distinct coordination sites (VI and VIII), we observe equal abundances of ferric ions (Fe3+) and ions having delocalized electrons (Fe-M), and only at higher pressures is a fully metallic high-pressure structure obtained, all at room temperature. Thereby, the transition is characterized by delocalization/metallization of the 3d electrons on half the Fe sites, with a site-dependent collapse of local moments. Above approximately 50 GPa, Fe2O3 is a strongly correlated metal with reduced electron mobility (large band renormalizations) of m*/m similar to 4 and 6 near the Fermi level. Importantly, upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition (Fe-VIII(3+HS) Fe-VI(M))O-3 -amp;gt;(50) (GPa)(Fe-VIII(3+HS) Fe-VI(3+HS))O-3 within the same P2(1)/n structure, indicating a decoupling of the electronic and lattice degrees of freedom. Our results offer a model for understanding insulator-metal transitions in correlated electron materials, showing that the interplay of electronic correlations and crystal structure may result in rather complex behavior of the electronic and magnetic states of such compounds.

  • 110.
    Wang, Fei
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Properties of multilayered and multicomponent nitride alloys from first principles2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is a theoretical exploration of properties of multilayered and multicomponent nitride alloys, in particular their mixing thermodynamics and elastic behaviors. Systematic investigation of properties of a large class of materials, such as the multicomponent nitride solid solutions, is in line with the modern approach of high-throughput search of novel materials. In this thesis we benchmark and utilize simple but efficient methodological frameworks in predicting mixing thermodynamics, Young’s moduli distribution of multilayer alloys and the linear thermal expansion of quaternary nitride solid solutions.

    We demonstrate by accurate ab-initio calculations that Ti1−xAlxN solid solution is stabilized by interfacial effects if it is coherently sandwiched between TiN layers along (001). For TiN/AlN and ZrN/AlN multilayers we show higher thermodynamic stability with semicoherent interfaces than with isostructural coherent ones.

    Accurate 0 Kelvin elastic constants of cubic TixXyAl1xyN (X=Zr, Hf, Nb, V, Ta) solid solutions and their multilayers are derived and an analytic comparison of strengths and ductility are presented to reveal the potential of these materials in hard coating applications. The Young’s moduli variation of the bulk materials has provided a reliable descriptor to screen the Young’s moduli of coherent multilayers.

    The Debye model is used to reveal the high-temperature thermodynamics and spinodal decomposition of TixNbyAl1−x−yN. We show that though the effect of vibration is large on the mixing Gibbs free energy the local spinoal decomposition tendencies are not altered. A quasi-harmonic Debye model is benchmarked against results of molecular dynamics simulations in predicting the thermal expansion coefficients of TixXyAl1xyN (X=Zr, Hf, Nb, V, Ta).  

    List of papers
    1. Special quasirandom structure method in application for advanced properties of alloys: A study on Ti0.5Al0.5N and TiN/Ti0.5Al0.5N multilayer
    Open this publication in new window or tab >>Special quasirandom structure method in application for advanced properties of alloys: A study on Ti0.5Al0.5N and TiN/Ti0.5Al0.5N multilayer
    2015 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 103, p. 194-199Article in journal (Refereed) Published
    Abstract [en]

    The special quasirandom structure (SQS) approach is a successful technique for modelling of alloys, however it breaks inherently the point symmetry of the underlying crystal lattice. We demonstrate that monocrystalline and polycrystalline elastic moduli can scatter significantly depending on the chosen SQS model and even on the supercell orientation in space. Also, we demonstrate that local disturbances, such as vacancies or interfaces change the SQS configuration in a way, that significantly affects the values of the calculated physical properties. Moreover, the diversity of local environments in random alloys results in a large variation of the calculated local properties. We underline that improperly chosen, generated or handled SQS may result in erroneous theoretical findings. The challenges of the SQS method are discussed using bulk Ti0.5Al0.5N alloy and TiN/Ti0.5Al0.5N multilayer as model systems. We present methodological corrections for the mindful application of this approach in studies of advanced properties of alloys.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Modelling alloys; Special quasirandom structure approach; Elastic constants; Vacancy formation energy; Multilayers
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-118022 (URN)10.1016/j.commatsci.2015.03.030 (DOI)000353377100024 ()
    Note

    Funding Agencies|SSF project Designed Multicomponent coatings, MultiFilms; Erasmus Mundus Programme of the European Commission within the Doctoral Programme DocMASE; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D.I. Mendeleev Fund Program; Swedish Research Council (VR)

    Available from: 2015-05-21 Created: 2015-05-20 Last updated: 2018-02-09
    2. Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
    Open this publication in new window or tab >>Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
    Show others...
    2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 17, p. 174201-Article in journal (Refereed) Published
    Abstract [en]

    In this work, we discuss the mixing thermodynamics of cubic (B1) Ti1-xAlxN/TiN(001) multilayers. We show that interfacial effects suppress the mixing enthalpy compared to bulk Ti1-xAlxN. The strongest stabilization occurs for compositions in which the mixing enthalpy of bulk Ti1-xAlxN has its maximum. The effect is split into a strain and an interfacial (or chemical) contribution, and we show that both contributions are significant. An analysis of the local atomic structure reveals that the Ti atoms located in the interfacial layers relax significantly different from those in the other atomic layers of the multilayer. Considering the electronic structure of the studied system, we demonstrate that the lower Ti-site projected density of states at epsilon(F) in the Ti1-xAlxN/TiN multilayers compared to the corresponding monolithic bulk explains a decreased tendency toward decomposition.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2016
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-129166 (URN)10.1103/PhysRevB.93.174201 (DOI)000375990200003 ()
    Note

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL [10-0026]; Erasmus Mundus Joint European Doctoral Programme DocMASE; Multiscale computational-design of novel hard nanostructure coatings; Swedish Research Council (VR) [2015-04391, 621-2012-4401, 2014-4750]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program [8.1.18.2015]; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

    Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2018-02-09
    3. Growth and thermal stability of TiN/ZrAlN: Effect of internal interfaces
    Open this publication in new window or tab >>Growth and thermal stability of TiN/ZrAlN: Effect of internal interfaces
    Show others...
    2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 121, p. 396-406Article in journal (Refereed) Published
    Abstract [en]

    Wear resistant hard films comprised of cubic transition metal nitride (c-TMN) and metastable c-AlN with coherent interfaces have a confined operating envelope governed by the limited thermal stability of metastable phases. However, equilibrium phases (c-TMN and wurtzite(w)-AlN) forming semicoherent interfaces during film growth offer higher thermal stability. We demonstrate this concept for a model multilayer system with TiN and ZrAlN layers where the latter is a nanocomposite of ZrN- and AlN-rich domains. The interfaces between the domains are tuned by changing the AlN crystal structure by varying the multilayer architecture and growth temperature. The interface energy minimization at higher growth temperature leads to formation of semicoherent interfaces between w-AlN and c-TMN during growth of 15 nm thin layers. Ab initio calculations predict higher thermodynamic stability of semicoherent interfaces between c-TMN and w-AlN than isostructural coherent interfaces between c-TMN and c-AlN. The combination of a stable interface structure and confinement of w-AlN to nm-sized domains by its low solubility in c-TMN in a multilayer, results in films with a stable hardness of 34 GPa even after annealing at 1150 degrees C. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    Pergamon Press, 2016
    Keywords
    Thermal stability, TM-Al-N multilayer films, Nanostructured materials, Interface energy, Three-dimensional atom probe (3DAP), Transmission electron microscopy
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-132827 (URN)10.1016/j.actamat.2016.07.006 (DOI)000386984500038 ()
    Note

    Funding Agencies|Swedish Research Council (VR grant) [621-2012-4401]; Swedish Foundation for Strategic Research (SSF) through the program MultiFilms [RMA08-0069]; Swedish government strategic research area grant in material science AFM - SFO MatLiU [2009-00971]; EUs Erasmus Mundus graduate school in Material Science and Engineering (DocMASE); Swedish Governmental Agency for Innovation Systems [VINNMer 2011-03464, 2013-02355]; EU-funded project AME-Lab (European Regional Development Fund) [C/4-EFRE-13/2009/Br]; DFG; federal state government of Saarland [INST 256/298-1 FUGG]

    Available from: 2016-12-06 Created: 2016-11-30 Last updated: 2018-02-09
    4. Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers
    Open this publication in new window or tab >>Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers
    Show others...
    2017 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 127, p. 124-132Article in journal (Refereed) Published
    Abstract [en]

    We give a comprehensive overview of the elastic properties of cubic quaternary transition metal nitride alloys and coherent nitride multilayers for design of wear resistant hard coatings. The elastic stiffness constants of the alloys are calculated using the special quasirandom structure method. For multilayers with sharp interfaces we prove the applicability of a linear-elasticity approximation and show that it can be used with success instead of performing direct computationally demanding ab initio calculations. We explore the trends and the potential of multicomponent alloying in engineering the strength and ductility of both, quaternary alloys and their multilayers. We investigate X(i-x-y)TixAlyN alloys where Xis Zr, Hf, V, Nb or Ta, and present an analysis based on increasing x. We show that with increasing Ti content ductility can increase in each alloy. Elastic isotropy is observed only in (Zr,Hf,V)((i-x-y))TixAlyN alloys in the middle of the compositional triangle, otherwise a high Youngs modulus is observed along [001]. We predict that coherent TiN/X(1-x-y)TixAlyN and ZrN/X(i-x-3)TixAlyN alloy multilayers with the [111] interfacial direction show increasing ductility with increasing x, while the multilayers with the [001] orientation become more brittle. We show that the Youngs moduli variation in the parent bulk quaternary nitride alloy provide a reliable descriptor to screen the Youngs modulus of coherent multilayers in high-throughput calculations. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    PERGAMON-ELSEVIER SCIENCE LTD, 2017
    Keywords
    Ab initio calculations; Elastic properties; Transition metal nitride alloys; Multicomponent; Multilayers
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-136865 (URN)10.1016/j.actamat.2017.01.017 (DOI)000397362600012 ()
    Note

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL Grant [10-0026]; MERA.NET [2013-02355]; Erasmus Mundus Joint European Doctoral Programme DocMASE; Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.000]

    Available from: 2017-04-30 Created: 2017-04-30 Last updated: 2018-02-09
  • 111.
    Hansson, Tobias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brescia, Italy.
    Parra-Rivas, Pedro
    Univ Libre Bruxelles, Belgium; Univ Leuven, Belgium.
    Bernard, Martino
    Univ Brescia, Italy.
    Leo, Francois
    Univ Libre Bruxelles, Belgium.
    Gelens, Lendert
    Univ Leuven, Belgium.
    Wabnitz, Stefan
    Univ Brescia, Italy; CNR INO, Italy.
    Quadratic soliton combs in doubly resonant second-harmonic generation2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 24, p. 6033-6036Article in journal (Refereed)
    Abstract [en]

    We report a theoretical investigation of quadratic frequency combs in a dispersive second-harmonic generation cavity system. We identify different dynamical regimes and demonstrate that the same system can exhibit both bright and dark localized cavity solitons in the absence of a temporal walk-off. (c) 2018 Optical Society of America

  • 112.
    Fallqvist, Amie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, National Supercomputer Centre (NSC). Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Belov, M. P.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Resolving the debated atomic structure of the metastable cubic SiNx tissue phase in nanocomposites with TiN2018In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 9, article id 093608Article in journal (Refereed)
    Abstract [en]

    The TiN/SiNx nanocomposite and nanolaminate systems are the archetype for super if not ultrahard materials. Yet, the nature of the SiNx tissue phase is debated. Here, we show by atomically resolved electron microscopy methods that SiNx is epitaxially stabilized in a NaCl structure on the adjacent TiN(001) surfaces. Additionally, electron energy loss spectroscopy, supported by first-principles density functional theory calculations infer that SiNx hosts Si vacancies.

  • 113.
    Ribeiro Jr, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    da Silva, Gesiel Gomes
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil; Goias Federal Institute of Science and Technology, IFG, Luziânia, Brazil.
    de Sousa Jr, Rafael Timoteo
    Department of Electrical Engineering, University of Brasίlia, Brasίlia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    da Cunha, Wiliam Ferreira
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    Magela e Silva, Geraldo
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    Spin-Orbit Effects on the Dynamical Properties of Polarons in Graphene Nanoribbons2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 1914Article in journal (Refereed)
    Abstract [en]

    The dynamical properties of polarons in armchair graphene nanoribbons (GNR) is numerically investigated in the framework of a two-dimensional tight-binding model that considers spin-orbit (SO) coupling and electron-lattice (e-l) interactions. Within this physical picture, novel polaron properties with no counterparts to results obtained from conventional tight-binding models are obtained. Our findings show that, depending on the systems width, the presence of SO coupling changes the polarons charge localization giving rise to different degrees of stability for the charge carrier. For instance, the joint action of SO coupling and e-l interactions could promote a slight increase on the charge concentration in the center of the lattice deformation associated to the polaron. As a straightforward consequence, this process of increasing stability would lead to a depreciation in the polarons motion by decreasing its saturation velocity. Our finds are in good agreement with recent experimental investigations for the charge localization in GNR, mostly when it comes to the influence of SO coupling. Moreover, the contributions reported here provide a reliable method for future works to evaluate spin-orbit influence on the performance of graphene nanoribbons.

  • 114.
    Ektarawong, Annop
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Stability of SnSe1-xSx solid solutions revealed by first-principles cluster expansion2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 29, article id 29LT01Article in journal (Refereed)
    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.

  • 115.
    Ektarawong, Annop
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Structural models of increasing complexity for icosahedral boron carbide with compositions throughout the single-phase region from first principles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 17, article id 174104Article in journal (Refereed)
    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.

  • 116.
    Burakovsky, Leonid
    et al.
    Los Alamos Natl Lab, NM 87545 USA.
    Burakovsky, Naftali
    Los Alamos Natl Lab, NM 87545 USA.
    Preston, Dean
    Los Alamos Natl Lab, NM 87545 USA.
    Simak, Sergei I
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Systematics of the Third Row Transition Metal Melting: The HCP Metals Rhenium and Osmium2018In: Crystals, ISSN 2073-4352, Vol. 8, no 6, article id 243Article in journal (Refereed)
    Abstract [en]

    The melting curves of rhenium and osmium to megabar pressures are obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. In addition, for Re, we combine QMD simulations with total free energy calculations to obtain its phase diagram. Our results indicate that Re, which generally assumes a hexagonal close-packed (hcp) structure, melts from a face-centered cubic (fcc) structure in the pressure range 20-240 GPa. We conclude that the recent DAC data on Re to 50 GPa in fact encompass both the true melting curve and the low-slope hcp-fcc phase boundary above a triple point at (20 GPa, 4240 K). A linear fit to the Re diamond anvil cell (DAC) data then results in a slope that is 2.3 times smaller than that of the actual melting curve. The phase diagram of Re is topologically equivalent to that of Pt calculated by us earlier on. Regularities in the melting curves of Re, Os, and five other 3rd-row transition metals (Ta, W, Ir, Pt, Au) form the 3rd-row transition metal melting systematics. We demonstrate how this systematics can be used to estimate the currently unknown melting curve of the eighth 3rd-row transition metal Hf.

  • 117.
    Fritton, Massimo
    et al.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Otte, Katrin
    Bavarian Acad Sci and Humanities, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Biswas, Pronay Kumar
    Univ Siegen, Germany.
    Heckl, Wolfgang M.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Schmittel, Michael
    Univ Siegen, Germany.
    Lackinger, Markus
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    The influence of ortho-methyl substitution in organometallic self-assembly - a comparative study on Cu(111) vs. Ag(111)2018In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 70, p. 9745-9748Article in journal (Refereed)
    Abstract [en]

    Metal surface-induced dehalogenation of precursors is known to initiate self-assembly of organometallic networks, where tectons are connected via carbon-metal-carbon (C-M-C) bonds. Even though reversibility of the C-M-C bonds facilitates structural equilibration, defects associated with highly bent organometallic linkages are still commonly observed. By introducing a steric hindrance to reduce the C-M-C bond angle flexibility, we find well ordered organometallic networks of an ortho-methyl substituted 1,3,5-tris(p-bromophenyl)-benzene analogue on Cu(111) after room-temperature (RT) deposition and on Ag(111) after annealing.

  • 118.
    Gharavi, Mohammad Amin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Theoretical study of phase stability, crystal and electronic structure of MeMgN2 (Me = Ti, Zr, Hf) compounds2018In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 53, no 6, p. 4294-4305Article in journal (Refereed)
    Abstract [en]

    Scandium nitride has recently gained interest as a prospective compound for thermoelectric applications due to its high Seebeck coefficient. However, ScN also has a relatively high thermal conductivity, which limits its thermoelectric efficiency and figure of merit (zT). These properties motivate a search for other semiconductor materials that share the electronic structure features of ScN, but which have a lower thermal conductivity. Thus, the focus of our study is to predict the existence and stability of such materials among inherently layered equivalent ternaries that incorporate heavier atoms for enhanced phonon scattering and to calculate their thermoelectric properties. Using density functional theory calculations, the phase stability of TiMgN2, ZrMgN2 and HfMgN2 compounds has been calculated. From the computationally predicted phase diagrams for these materials, we conclude that all three compounds are stable in these stoichiometries. The stable compounds may have one of two competing crystal structures: a monoclinic structure (LiUN2 prototype) or a trigonal superstructure (NaCrS2 prototype; RmH). The band structure for the two competing structures for each ternary is also calculated and predicts semiconducting behavior for all three compounds in the NaCrS2 crystal structure with an indirect band gap and semiconducting behavior for ZrMgN2 and HfMgN2 in the monoclinic crystal structure with a direct band gap. Seebeck coefficient and power factors are also predicted, showing that all three compounds in both the NaCrS2 and the LiUN2 structures have large Seebeck coefficients. The predicted stability of these compounds suggests that they can be synthesized by, e.g., physical vapor deposition.

  • 119.
    Tasnadi, Ferenc
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Wang, Fei
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Saarland Univ, Germany.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Thermal expansion of quaternary nitride coatings2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 13, article id 135901Article in journal (Refereed)
    Abstract [en]

    The thermal expansion coefficient of technologically relevant multicomponent cubic nitride alloys are predicted using the Debye model with ab initio elastic constants calculated at 0 K and an isotropic approximation for the Gruneisen parameter. Our method is benchmarked against measured thermal expansion of TiN and Ti(1-x)AlxN as well as against results of molecular dynamics simulations. We show that the thermal expansion coefficients of Ti(1-x-y)XyAlxN (X = Zr, Hf, Nb, V, Ta) solid solutions monotonously increase with the amount of alloying element X at all temperatures except for Zr and Hf, for which they instead decrease for y greater than or similar to 0.5.

  • 120.
    Ektarawong, Annop
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Thermodynamic consideration and ground-state search of icosahedral boron subselenide B-12(B1-xSex)(2) from a first-principles cluster expansion2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 17, article id 174103Article in journal (Refereed)
    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.

  • 121.
    Spektor, Kristina
    et al.
    ESRF, France.
    Crichton, Wilson A.
    ESRF, France.
    Konar, Sumit
    Univ Edinburgh, Scotland; Univ Edinburgh, Scotland.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Unraveling Hidden Mg-Mn-H Phase Relations at High Pressures and Temperatures by in Situ Synchrotron Diffraction2018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 3, p. 1614-1622Article in journal (Refereed)
    Abstract [en]

    The MgMnH system was investigated by in situ high pressure studies of reaction mixtures MgH2MnH2. The formation conditions of two complex hydrides with composition Mg3MnH7 were established. Previously known hexagonal Mg3MnH7 (h-Mg3MnH7) formed at pressures 1.52 GPa and temperatures between 480 and 500 degrees C, whereas an orthorhombic form (o-Mg3MnH7) was obtained at pressures above 5 GPa and temperatures above 600 degrees C. The crystal structures of the polymorphs feature octahedral [Mn(I)H-6](5) complexes and interstitial H-. Interstitial H- is located in trigonal bipyramidal and square pyramidal interstices formed by Mg2+ ions in h- and o-Mg3MnH7, respectively. The hexagonal form can be retained at ambient pressure, whereas the orthorhombic form upon decompression undergoes a distortion to monoclinic Mg3MnH7 (m-Mg3MnH7). The structure elucidation of o- and m-Mg3MnH7 was aided by first-principles density functional theory (DFT) calculations. Calculated enthalpy versus pressure relations predict m- and o-Mg3MnH7 to be more stable than h-Mg3MnH7 above 4.3 GPa. Phonon calculations revealed o-Mg3MnH7 to be dynamically unstable at pressures below 5 GPa, which explains its phase transition to m-Mg3MnH7 on decompression. The electronic structure of the quenchable polymorphs h- and m-Mg3MnH7 is very similar. The stable 18-electron complex [MnH6](5-) is mirrored in the occupied states, and calculated band gaps are around 1.5 eV. The study underlines the significance of in situ investigations for mapping reaction conditions and understanding phase relations for hydrogen-rich complex transition metal hydrides.

  • 122.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    A simple electron plasma wave2017In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 381, no 11, p. 1033-1035Article in journal (Refereed)
    Abstract [en]

    Considering a class of solutions where the density perturbations are functions of time, but not of space, we derive a new exact large amplitude wave solution for a cold uniform electron plasma. This result illustrates that most simple analytical solutions can appear even if the density perturbations are large. (C) 2016 Elsevier B.V. All rights reserved.

  • 123.
    Finzel, Kati
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Baranov, Alexey I.
    Max Planck Institute Chemistry Phys Solids, Germany.
    A simple model for the Slater exchange potential and its performance for solids2017In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 117, no 1, p. 40-47Article in journal (Refereed)
    Abstract [en]

    A simple local model for the Slater exchange potential is determined by least square fit procedure from Hartree-Fock (HF) atomic data. Since the Slater potential is the exact exchange potential yielding HF electron density from Levy-Perdew-Sahni density functional formalism (Levy et al., Phys. Rev. A 1984, 30, 2745), the derived local potential is significantly more negative than the conventional local density approximation. On the set of 22 ionic, covalent and van der Waals solids including strongly correlated transition metal oxides, it has been demonstrated, that this simple model potential is capable of reproducing the band gaps nearly as good as popular meta GGA potentials in close agreement with experimental values.

  • 124.
    Mosyagin, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Lugovskoy, A. V.
    NUST MISIS, Russia.
    Krasilnikov, O. M.
    NUST MISIS, Russia.
    Vekilov, Yu. Kh.
    NUST MISIS, Russia; NUST MISIS, Russia.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach2017In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 220, p. 20-30Article in journal (Refereed)
    Abstract [en]

    We present a description of a technique for ab initio calculations of the pressure dependence of second and third-order elastic constants. The technique is based on an evaluation of the corresponding Lagrangian stress tensor derivative of the total energy assuming finite size of the deformations. Important details and parameters of the calculations are highlighted. Considering body-centered cubic Mo as a model system, we demonstrate that the technique is highly customizable and can be used to investigate non-linear elastic properties under high-pressure conditions. (C) 2017 Elsevier B.V. All rights reserved.

  • 125.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    About the compatibility between ansatzes and constraints for a local formulation of orbital-free density functional theory2017In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 117, no 5, article id UNSP e25329Article in journal (Refereed)
    Abstract [en]

    Functional properties that are exact for the Hohenberg-Kohn functional may turn into mutually exclusive constraints at a given level of ansatz. This is exemplarily shown for the local density approximation. Nevertheless, it is possible to reach exactly the Kohn-Sham data from an orbital-free density functional framework based on simple one-point functionals by starting from the Levy-Perdew-Sahni formulation. The energy value is obtained from the density-potential pair, and therefore does not refer to the functional dependence of the potential expression. Consequently, the potential expression can be obtained from any suitable model and is not required to follow proper scaling behavior.

  • 126.
    Green, B. L.
    et al.
    University of Warwick, England.
    Breeze, B. G.
    University of Warwick, England.
    Rees, G. J.
    University of Warwick, England.
    Hanna, J. V.
    University of Warwick, England.
    Chou, J. -P.
    Hungarian Academic Science, Hungary.
    Ivady, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Gali, A.
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Newton, M. E.
    University of Warwick, England.
    All-optical hyperpolarization of electron and nuclear spins in diamond2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 5, article id 054101Article in journal (Refereed)
    Abstract [en]

    Low thermal polarization of nuclear spins is a primary sensitivity limitation for nuclear magnetic resonance. Here we demonstrate optically pumped (microwave-free) nuclear spin polarization of C-13 and N-15 in N-15-doped diamond. (15)Npolarization enhancements up to- 2000 above thermal equilibrium are observed in the paramagnetic system Ns(0). Nuclear spin polarization is shown to diffuse to bulk C-13 with NMR enhancements of -200 at room temperature and -500 at 240 K, enabling a route to microwave-free high-sensitivity NMR study of biological samples in ambient conditions.

  • 127.
    Wretborn, Joel
    et al.
    DreamWorks Animation, Glendale, USA.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Museth, Ken
    DreamWorks Animation, Glendale, USA.
    Animation of crack propagation by means of an extended multi-body solver for the material point method2017In: Computers & graphics, ISSN 0097-8493, E-ISSN 1873-7684, Vol. 69, p. 131-139Article in journal (Refereed)
    Abstract [en]

    We propose a multi-body solver that extends the Material Point Method (MPM) to simulate cracks in computer animation. We define cracks as the intersection between pieces of bodies created by a pre-fracture process and held together by massless particle constraints (glue particles). These pieces are simulated using a MPM multi-body solver extended by us to efficiently handle N-body collisions. Benefits of the present work include (1) low computational overhead compared to a normal MPM algorithm; (2) good scaling in three dimensions due to our use of sparse grids for background computations; (3) allowing for an easy and controllable setup phase to simulate a desired material failure mode, which is especially useful for computer animation. 

  • 128.
    Sun, Weiwei
    et al.
    Uppsala University, Sweden; KTH Royal Institute Technology, Sweden.
    Luo, Wei
    Uppsala University, Sweden.
    Feng, Qingguo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ahuja, Rajeev
    Uppsala University, Sweden; KTH Royal Institute Technology, Sweden.
    Anisotropic distortion and Lifshitz transition in alpha-Hf under pressure2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 11, article id 115130Article in journal (Refereed)
    Abstract [en]

    In this work we report a theoretical investigation on behavior of the elastic constant C-44 and the transverse optical phonon mode E(2)g of a-Hf under pressure within the density functional theory. In contrast to many other reported transition metals, the above two quantities do not show a synchronous relation as pressure increases. Below 13 GPa, an opposite shifting tendency has been observed. However, once the pressure is raised above 13 GPa, the trend is pulled back to be consistent. This anomalous behavior is figured out to be caused by the large lattice anisotropy of the c/a ratio along with the elastic anisotropy. The synchronous behavior is found to be in accordance with the behavior of c/a ratio with increased pressure. In our band-structure investigations the electronic topological transition has been discovered at 10 GPa, which relates to the change of c/a ratio suggested by recent literature. The presence of the Van Hove singularity shown in the densities of states has been identified and regarded as the origin of the variation of C-44 and E(2)g.

  • 129.
    Marcus, Carina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Saab AB, SE-58188 Linkoping, Sweden.
    Andersson, Kent
    Swedish Def University, Sweden; National Def University, Finland.
    Åkerlind, Christina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Swedish Def Research Agency, Sweden.
    Balancing the radar and long wavelength infrared signature properties in concept analysis of combat aircraft - A proof of concept2017In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 71, p. 733-741Article in journal (Refereed)
    Abstract [en]

    Designing combat aircraft with high military effectiveness, affordability and military suitability requires balancing the efforts of many engineering disciplines during all phases of the development. One particular challenge is aircraft survivability, the aircrafts ability to avoid or withstand hostile actions. Signature management is one way of increasing the survivability by improving the ability to avoid detection. Here, the long-wave infrared and radar signatures are studied simultaneously in a mission context. By establishing a system of systems approach at mission system level, the risk of sub optimization at a technical level is greatly reduced. A relevant scenario is presented where the aim is to incapacitate an air-defense system using three different tactics: A low-altitude cruise missile option, a low and medium altitude combat aircraft option. The technical sub-models, i.e. the properties of the signatures, the weapons and the sensors are modeled to a level suitable for early concept development. The results from the scenario simulations are useful for a relative comparison of properties. Depending on the situation, first detection is made by either radar or infrared sensors. Although the modeling is basic, the complexity of the infrared signature and detection chain is demonstrated and possible pivot points for the balancing of radar and IR signature requirements are identified. The evaluation methodology can be used for qualitative evaluation of aircraft concepts at different design phases, provided that the technical models are adapted to a suitable level of detail. (C) 2017 Elsevier Masson SAS. All rights reserved.

  • 130.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Bloch oscillations in organic and inorganic polymers2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 14, article id 144903Article in journal (Refereed)
    Abstract [en]

    The transport of polarons above the mobility threshold in organic and inorganic polymers is theoretically investigated in the framework of a one-dimensional tight-binding model that includes lattice relaxation. The computational approach is based on parameters for which the model Hamiltonian suitably describes different polymer lattices in the presence of external electric fields. Our findings show that, above critical field strengths, a dissociated polaron moves through the polymer lattice as a free electron performing Bloch oscillations. These critical electric fields are considerably smaller for inorganic lattices in comparison to organic polymers. Interestingly, for inorganic lattices, the free electron propagates preserving charge and spin densities localization which is a characteristic of a static polaron. Moreover, in the turning points of the spatial Bloch oscillations, transient polaron levels are formed inside the band gap, thus generating a fully characterized polaron structure. For the organic case, on the other hand, no polaron signature is observed: neither in the shape of the distortion-those polaron profile signatures are absent-nor in the energy levels-as no such polaron levels are formed during the simulation. These results solve controversial aspects concerning Bloch oscillations recently reported in the literature and may enlighten the understanding about the charge transport mechanism in polymers above their mobility edge. Published by AIP Publishing.

  • 131.
    Aschebrock, Thilo
    et al.
    University of Bayreuth, Germany.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Kuemmel, Stephan
    University of Bayreuth, Germany.
    Challenges for semilocal density functionals with asymptotically nonvanishing potentials2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075140Article in journal (Refereed)
    Abstract [en]

    The Becke-Johnson model potential [A. D. Becke and E. R. Johnson, J. Chem. Phys. 124, 221101 ( 2006)] and the potential of the AK13 functional [R. Armiento and S. Kummel, Phys. Rev. Lett. 111, 036402 ( 2013)] have been shown to mimic features of the exact Kohn-Sham exchange potential, such as step structures that are associated with shell closings and particle-number changes. A key element in the construction of these functionals is that the potential has a limiting value far outside a finite system that is a system-dependent constant rather than zero. We discuss a set of anomalous features in these functionals that are closely connected to the nonvanishing asymptotic potential. The findings constitute a formidable challenge for the future development of semilocal functionals based on the concept of a nonvanishing asymptotic constant.

  • 132.
    Jones, A.
    et al.
    Department of Electrical Engineering and Computing Systems, University of Cincinnati, Cincinnati, Ohio 45221, USA.
    Cahay, M.
    Department of Electrical Engineering and Computing Systems, University of Cincinnati, Cincinnati, Ohio 45221, USA.
    Yakimenko, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Chapter 5: Signatures of Spin Polarization In Four-Gate Quantum Point Contact Structures2017In: Contemporary Topics in Semiconductor Spintronics, World Scientific, 2017, p. 123-158Chapter in book (Refereed)
    Abstract [en]

    Using a Non-equilibrium Green’s function (NEGF) approach, a set of experiments is suggested which can provide indirect evidence of the fine and non-local electrostatic tuning of the onset of spin polarization in two closely spaced quantum point contacts (QPCs) with two sets of in-plane side gates (SGs) in the presence of lateral spin-orbit coupling (LSOC). The conductance of the two closely spaced QPCs or four-gate QPC is studied for different biasing conditions applied to two leftmost and rightmost SGs. When calculated as a function of the common sweep voltage Vsweep applied to two of the SGs, the conductance plots show several conductance anomalies, i.e., below G0 = 2e2/h, characterized by intrinsic bistability, i.e., hysteresis loops due to a difference in the conductance curves for up and down sweeps of the common gate voltage. The hysteresis loops are related to the co-existence of multistable spin textures in the narrow channel of the four-gate QPC and are very sensitive to the biasing conditions on the four SGs. The shape of the conductance anomalies and size of hysteresis loops are different when the biasing conditions on the leftmost and rightmost SGs are swapped. This rectifying behavior is an additional indirect evidence for the onset of spontaneous spin polarization in nanoscale devices made of QPCs. These results show that the onset and fine tuning of conductance anomalies in QPC structures are highly sensitive to the non-local action of closely spaced SGs. This effect must therefore be taken into account in the design of all electrical spin valves making use of middle gates to fine tune the spin precession between QPC based spin injector and detector contacts.

  • 133.
    Skripnyak, Natalia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University, Russia.
    Emelyanova, E. S.
    National Research Tomsk State University, Russia.
    Skripnyak, V. A.
    National Research Tomsk State University, Russia.
    Skripnyak, E. G.
    National Research Tomsk State University, Russia.
    Damage of High-Chromium Steels under Deformation in a Wide Temperature Range2017In: PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2017 (AMHS17), AMER INST PHYSICS , 2017, Vol. 1909, article id UNSP 020200Conference paper (Refereed)
    Abstract [en]

    High-chromium steels have high strength properties, corrosion properties and resistance to neutron irradiation, thereby are considered as promising steels for nuclear reactors of generation IV. The deformation and damage of high chromium steels in a wide temperature range was studied by numerical simulation method. A model was proposed to predict the deformation and damage of high chromium steels under quasi-static loading within the temperature range from 295 to 1100 K. It is shown that the ductility of high-chromium steels increases proportionally to temperature in the range from 750 to 1100 K due to the growth of alpha-phase precipitates.

  • 134.
    Skripnyak, Vladimir A.
    et al.
    Natl Res Tomsk State Univ TSU, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Res Tomsk State Univ TSU, Russia.
    Skripnyak, Vladimir V.
    Natl Res Tomsk State Univ TSU, Russia.
    Skripnyak, Evgeniya G.
    Natl Res Tomsk State Univ TSU, Russia.
    DEFORMATION AND DAMAGE OF Fe-Cr STEELS IN A WIDE TEMPERATURE RANGE2017In: PROCEEDINGS OF THE 7TH INTERNATIONAL CONFERENCE ON MECHANICS AND MATERIALS IN DESIGN (M2D2017), INEGI-FEUP , 2017, p. 1763-1772Conference paper (Refereed)
    Abstract [en]

    The deformation and damage of a high chromium steels in a wide temperature range was studied by numerical simulation method. A model was proposed to predict the deformation and damage of high chromium steels at a quasi-static loading within the temperature range from 295 K to 1100 K. The model takes into consideration mechanisms of hardening and softening high chromium steels in a wide temperature range. It is shown that the ductility of high-chromium steels increases proportional to temperature in the range from 750 K to 1100 K in connection with the growth of precipitates of alpha-phase.

  • 135.
    Mosyagin, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Development and applications of theoretical algorithms for simulations of materials at extreme conditions2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Materials at extreme conditions exhibit properties that differ substantially from ambient conditions. High pressure and high temperature expose anharmonic, non-linear behavior, and can provoke phase transitions among other effects. Experimental setups to study that sort of effects are typically costly and experiments themselves are laborious. It is common to apply theoretical techniques in order to provide a road-map for experimental research. In this thesis I cover computational algorithms based on first-principles calculations for high-temperature and high-pressure conditions. The two thoroughly described algorithms are: 1) the free energy studies using temperature-dependent effective potential method (TDEP), and 2) a higher-order elastic constants calculation procedure. The algorithms are described in an easy to follow manner with motivation for every step covered.

    The Free energy calculation algorithm is demonstrated with applications to hexagonal close-packed Iron at the conditions close to the inner Earth Core’s. The algorithm of elastic constants calculation is demonstrated with application to Molybdenum, Tantalum, and Niobium. Other projects included in the thesis are the study of effects of van der Waals corrections on the graphite and diamond equations of state.

    List of papers
    1. Highly Efficient Free Energy Calculations of the Fe Equation of State Using Temperature-Dependent Effective Potential Method
    Open this publication in new window or tab >>Highly Efficient Free Energy Calculations of the Fe Equation of State Using Temperature-Dependent Effective Potential Method
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    2016 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 43, p. 8761-8768Article in journal (Refereed) Published
    Abstract [en]

    Free energy calculations at finite temperature based on ab initio molecular dynamics (AIMD) simulations have become possible, but they are still highly computationally demanding. Besides, achieving simultaneously high accuracy of the calculated results and efficiency of the computational algorithm is still a challenge. In this work we describe an efficient algorithm to determine accurate free energies of solids in simulations using the recently proposed temperature-dependent effective potential method (TDEP). We provide a detailed analysis of numerical approximations employed in the TDEP algorithm. We show that for a model system considered in this work, hcp Fe, the obtained thermal equation of state at 2000 K is in excellent agreement with the results of standard calculations within the quasiharmonic approximation.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2016
    National Category
    Theoretical Chemistry
    Identifiers
    urn:nbn:se:liu:diva-132993 (URN)10.1021/acs.jpca.6b08633 (DOI)000387198600028 ()27700093 (PubMedID)
    Note

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) program SRL [10-0026]; Swedish Research Council (VR) [2015-04391, 2014-4750, 637-2013-7296]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; PRACE-2IP project [FP7 RI-283493]

    Available from: 2016-12-09 Created: 2016-12-07 Last updated: 2017-04-24Bibliographically approved
    2. Theoretical description of pressure-induced phase transitions: a case study of Ti-V alloys
    Open this publication in new window or tab >>Theoretical description of pressure-induced phase transitions: a case study of Ti-V alloys
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    2015 (English)In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 35, no 1, p. 42-48Article in journal (Refereed) Published
    Abstract [en]

    We discuss theoretical description of pressure-induced phase transitions by means of first-principles calculations in the framework of density functional theory. We illustrate applications of theoretical tools that allow one to take into account configurational and vibrational disorders, considering Ti-V alloys as a model system. The universality of the first-principles theory allows us to apply it in studies of different phenomena that occur in the Ti-V system upon compression. Besides the transitions between different crystal structures, we discuss isostructural transitions in bcc Ti-V alloys. Moreover, we present arguments for possible electronic transitions in this system, which may explain peculiar behaviour of elastic properties of V upon compression.

    Place, publisher, year, edition, pages
    Taylor andamp; Francis: STM, Behavioural Science and Public Health Titles, 2015
    Keywords
    phase stability; first-principles calculations; Ti-V alloys; high pressure
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-114586 (URN)10.1080/08957959.2014.992896 (DOI)000348672100007 ()
    Note

    Funding Agencies|Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; SSF [SRL 10-0026]; Russian Foundation for Basic Researches [13-02-00606a]; Tomsk State University Academic D.I. Mendeleev Fund Program; Program of Fundamental Research of State Academies of Sciences

    Available from: 2015-02-27 Created: 2015-02-26 Last updated: 2017-12-04
    3. Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics
    Open this publication in new window or tab >>Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics
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    2013 (English)In: TMS2013 Supplemental Proceedings, John Wiley & Sons, 2013, p. 617-626Chapter in book (Refereed)
    Abstract [en]

    Ab initio electronic structure theory is known as a useful tool for prediction of materials properties. However, majority of simulations still deal with calculations in the framework of density functional theory with local or semi-local functionals carried out at zero temperature. We present new methodological solution.s, which go beyond this approach and explicitly take finite temperature, magnetic, and many-body effects into account. Considering Ti-based alloys, we discuss !imitations of the quasiharmonic approximation for the treatment of lattice vibrations, and present an accurate and easily extendable method to calculate free ,energies of strongly anharmonic solids. We underline the necessity to going beyond the state-of-the-art techniques for the determination of effective cluster interactions in systems exhibiting mctal-to-insulator transition, and describe a unified cluster expansion approach developed for this class of materials. Finally, we outline a first-principles method, disordered local moments molecular dynamics, for calculations of thermodynamic properties of magnetic alloys, like Cr1-x,.AlxN, in their high-temperature paramagnetic state. Our results unambiguously demonstrate importance of finite temperature effects in theoretical calculations ofthermodynamic properties ofmaterials.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2013
    Keywords
    Alloy thermodynamics, Ti alloys, (Ti-Al)N, (Cr-Al)N
    National Category
    Condensed Matter Physics Theoretical Chemistry Inorganic Chemistry Metallurgy and Metallic Materials
    Identifiers
    urn:nbn:se:liu:diva-136443 (URN)10.1002/9781118663547.ch77 (DOI)9781118605813 (ISBN)9781118663547 (ISBN)
    Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-11-01Bibliographically approved
  • 136.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr University of Bochum, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Effects of incident N atom kinetic energy on TiN/TiN(001) film growth dynamics: A molecular dynamics investigation2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 2, article id 025302Article in journal (Refereed)
    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.

  • 137.
    Cirera, B.
    et al.
    IMDEA Nanosci, Spain.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Otero, R.
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain.
    Gallego, J. M.
    CSIC, Spain.
    Miranda, R.
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain.
    Ecija, D.
    IMDEA Nanosci, Spain.
    Efficient Lanthanide Catalyzed Debromination and Oligomeric Length-Controlled Ullmann Coupling of Aryl Halides2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 14, p. 8033-8041Article in journal (Refereed)
    Abstract [en]

    Lanthanide elements play a vital role in a broad range of high-tech applications, and there is an increasing interest in their catalytic activity, particularly in organo-metallics. However, their catalytic role on surfaces remains unexplored. Here, we present a scanning tunneling microscopy and density functional theory study of the debromination, contacting, and coupling of dibromine terphenyl species with Dy (f-block element) and Ag (d-block element) adatoms, respectively. We show that Dy debrominates the targeted species more efficiently than Ag adatoms at room temperature, promoting the formation of unprecedented C-Dy-C organo-metallic supramolecules versus C-Ag-C parallel chains for the Ag case. DFT calculations corroborate our results showing an almost spontaneous debromination process with Dy compared to Ag. Upon annealing, for samples containing Dy, the formation of C-Ag-C organometallic bonds and concomitant C-C coupling is inhibited, giving rise to a self-assembly of debrominated monomers, showing only a minority number of covalent dimes species. For samples without Dy covalent chains of irregular length are promoted. Our studies open new avenues for using lanthanide elements as efficient dehalogenation catalysts. Furthermore, we illustrate their potential as inhibitors of uncontrolled C-C coupling reactions, of great relevance for fine-tuning the length of polymeric compounds.

  • 138.
    Pourovskii, L. V.
    et al.
    University of Paris Saclay, France; Coll France, France; National University of Science and Technology MISIS, Russia.
    Mravlje, J.
    Jozef Stefan Institute, Slovenia.
    Georges, A.
    University of Paris Saclay, France; Coll France, France; University of Geneva, Switzerland.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Electron-electron scattering and thermal conductivity of epsilon-iron at Earths core conditions2017In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, article id 073022Article in journal (Refereed)
    Abstract [en]

    The electronic state and transport properties of hot dense iron are of the utmost importance for the understanding of Earths interior. Combining state-of-the-art density functional and dynamical mean field theories we study the impact of electron correlations on the electrical and thermal resistivity of hexagonal close-packed epsilon-Fe at Earths core conditions and show that the electron-electron scattering in epsilon-Fe exhibit a nearly perfect Fermi-liquid (FL) behavior. Accordingly, the quadratic dependence of the scattering rate, typical of FLs, leads to a modification of the Wiedemann-Franz law and suppresses the thermal conductivity with respect to the electrical one. The consequence is a significant increase of the electron-electron thermal resistivity, which is found to be of comparable magnitude to the electron-phonon one.

  • 139.
    Mikula, Marian
    et al.
    Comenius University, Slovakia; Slovak Academic Science, Slovakia.
    Truchly, Martin
    Comenius University, Slovakia.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr University of Bochum, Germany.
    Plasienka, Dusan
    Comenius University, Slovakia.
    Roch, Tomas
    Comenius University, Slovakia.
    Gregor, Maros
    Comenius University, Slovakia.
    Durina, Pavol
    Comenius University, Slovakia.
    Janik, Marian
    Comenius University, Slovakia.
    Kus, Peter
    Comenius University, Slovakia.
    Experimental and computational studies on toughness enhancement in Ti-Al-Ta-N quaternaries2017In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 35, no 6, article id 060602Article in journal (Refereed)
    Abstract [en]

    Design of hard ceramic material coatings with enhanced toughness, which prevents crack formation/propagation leading to brittle failure during application, is a primary industrial requirement. In this work, experimental methods supported by ab initio density functional theory (DFT) calculations and electronic structure analyses are used to investigate the mechanical behavior of magnetron sputtered Ti-Al-Ta-N hard coatings. The as-deposited Ti1-x-yAlxTayN (y = 0-0.60) films exhibit a single phase cubic sodium chloride (B1) structure identified as TiAl(Ta)N solid solutions. While the hardness H of Ti0.46Al0.54N (32.5 +/- 2 GPa) is not significantly affected by alloying with TaN (H of the quaternary nitrides varies between 26 +/- 2 and 35 +/- 4 GPa), the elastic stiffness monotonically decreases from 442 to 354 GPa with increasing Ta contents, which indicates improved toughness in TiAlTaN. Consistent with the experimental findings, the DFT results show that Ta substitutions in TiAlN reduce the shear resistance due to the enhanced occupation of metal-metal bonding states while preserving strong metal-N bonds. The metal-N bonding character, however, is progressively modified from prevalently ionic (TiAlN) toward more covalent (TiAlTaN). (C) 2017 American Vacuum Society.

  • 140.
    Wang, Xiao-Ye
    et al.
    Max Planck Institute Polymer Research, Germany.
    Richter, Marcus
    Technical University of Dresden, Germany.
    He, Yuanqin
    Technical University of Munich, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Riss, Alexander
    Technical University of Munich, Germany.
    Rajesh, Raju
    Max Planck Institute Polymer Research, Germany.
    Garnica, Manuela
    Technical University of Munich, Germany.
    Hennersdorf, Felix
    Technical University of Dresden, Germany.
    Weigand, Jan J.
    Technical University of Dresden, Germany.
    Narita, Akimitsu
    Max Planck Institute Polymer Research, Germany.
    Berger, Reinhard
    Technical University of Dresden, Germany.
    Feng, Xinliang
    Technical University of Dresden, Germany.
    Auwaerter, Willi
    Technical University of Munich, Germany.
    Barth, Johannes V.
    Technical University of Munich, Germany.
    Palma, Carlos-Andres
    Technical University of Munich, Germany.
    Muellen, Klaus
    Max Planck Institute Polymer Research, Germany.
    Exploration of pyrazine-embedded antiaromatic polycyclic hydrocarbons generated by solution and on-surface azomethine ylide homocoupling2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 1948Article in journal (Refereed)
    Abstract [en]

    Nanographenes, namely polycyclic aromatic hydrocarbons (PAHs) with nanoscale dimensions (amp;gt;1 nm), are atomically precise cutouts from graphene. They represent prime models to enhance the scope of chemical and physical properties of graphene through structural modulation and functionalization. Defined nitrogen doping in nanographenes is particularly attractive due to its potential for increasing the number of p-electrons, with the possibility of introducing localized antiaromatic ring elements. Herein we present azomethine ylide homocoupling as a strategy to afford internally nitrogen-doped, non-planar PAH in solution and planar nanographene on surfaces, with central pyrazine rings. Localized antiaromaticity of the central ring is indicated by optical absorption spectroscopy in conjunction with theoretical calculations. Our strategy opens up methods for chemically tailoring graphene and nanographenes, modified by antiaromatic dopants.

  • 141.
    Yalamanchili, K.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Wang, Fei
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Saarland University, Germany.
    Schramm, Isabella
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Saarland University, Germany.
    Andersson, J. M.
    Seco Tools AB, Sweden.
    Johansson Jöesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Seco Tools AB, Sweden.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Muecklich, F.
    Saarland University, Germany.
    Ghafoor, Naureen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Exploring the high entropy alloy concept in (AlTiVNbCr)N2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 636, p. 346-352Article in journal (Refereed)
    Abstract [en]

    We have explored the high entropy alloy (HEA) concept in the AlTiVNbCr-nitride material system. (AlTiVNbCr)N coatings synthesized by reactive cathodic arc deposition are close to an ideal cubic solid solution with a positive mean-field enthalpy of mixing of 0.06 eV/atom. First principle calculations showa higher thermodynamic stability for the solid solution relative to their binaries thereby indicating a possible entropy stabilization at a temperature above 727 degrees C. However, the elevated temperature annealing experiments show that the solid solution decomposes to w-AlN and c-(TiVNbCr)N. The limited thermal stability of the solid solution is investigated in relation to several thermodynamic parameters. We suggest that the HEA designed multiprincipal element (AlTiVNbCr) N solid solutions are in a metastable state. (C) 2017 Published by Elsevier B.V.

  • 142.
    Ektarawong, Annop
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
    First-principles prediction of stabilities and instabilities of compounds and alloys in the ternary B-As-P system2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 2, article id 024202Article in journal (Refereed)
    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.

  • 143.
    Brodin, Gert
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Juul Rasmussen, Jens
    Technical University of Denmark, Denmark.
    Focus issue to honour Hans L Pecseli on his 70th birthday2017In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 92, no 1, article id 010301Article in journal (Other academic)
    Abstract [en]

    n/a

  • 144.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Hybrid-DFT + V-w method for band structure calculation of semiconducting transition metal compounds: the case of cerium dioxide2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 45, article id 454002Article in journal (Refereed)
    Abstract [en]

    Hybrid functionals non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT + V-w method (Ivady et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT + V-w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA + U, and therefore allowing for a demonstration of the advantages of the proposed scheme.

  • 145.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Davidsson, Joel
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    National Institute Quantum and Radiol Science and Technology, Japan.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Identification of Si-vacancy related room-temperature qubits in 4H silicon carbide2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 16, article id 161114Article in journal (Refereed)
    Abstract [en]

    The identification of a microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, silicon-vacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin-3/2 ground and excited states. Although, these centers were observed decades ago, two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett. 115, 247602 (2015)], are still argued as an origin. By means of high-precision first-principles calculations and high-resolution electron spin resonance measurements, we here unambiguously identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Si-vacancy qubit configurations that provide room-temperature optical readout.

  • 146.
    Skripnyak, Vladimir A.
    et al.
    National Research Tomsk State University of TSU, Russia; Russian Academic Science, Russia; National Research Tomsk Polytech University of TPU, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University of TSU, Russia.
    Skripnyak, Evgeniya G.
    National Research Tomsk State University of TSU, Russia.
    Skripnyak, Vladimir V.
    National Research Tomsk State University of TSU, Russia; Russian Academic Science, Russia; National Research Tomsk Polytech University of TPU, Russia.
    Influence of Grain Size Distribution on the Mechanical Behavior of Light Alloys in Wide Range of Strain Rates2017In: SHOCK COMPRESSION OF CONDENSED MATTER - 2015: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, AMER INST PHYSICS , 2017, Vol. 1793, article id UNSP 110001Conference paper (Refereed)
    Abstract [en]

    Inelastic deformation and damage at the mesoscale level of ultrafine grained (UFG) light alloys with distribution of grain size were investigated in wide loading conditions by experimental and computer simulation methods. The computational multiscale models of representative volume element (RVE) with the unimodal and bimodal grain size distributions were developed using the data of structure researches aluminum and magnesium UFG alloys. The critical fracture stress of UFG alloys on mesoscale level depends on relative volumes of coarse grains. Microcracks nucleation at quasi-static and dynamic loading is associated with strain localization in UFG partial volumes with bimodal grain size distribution. Microcracks arise in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength.

  • 147.
    Skripnyak, Natalia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Res Tomsk State Univ TSU, Russia.
    Skripnyak, Evgeniya G.
    Natl Res Tomsk State Univ TSU, Russia.
    Skripnyak, Vladimir V.
    Natl Res Tomsk State Univ TSU, Russia.
    Skripnyak, Vladimir A.
    Natl Res Tomsk State Univ TSU, Russia.
    INFLUENCE OF GRAIN SIZE DISTRIBUTION ON THE MECHANICAL BEHAVIOR OF MATERIALS IN A WIDE RANGE OF STRAIN RATES2017In: PROCEEDINGS OF THE 7TH INTERNATIONAL CONFERENCE ON MECHANICS AND MATERIALS IN DESIGN (M2D2017), INEGI-FEUP , 2017, p. 1749-1762Conference paper (Refereed)
    Abstract [en]

    This work compares the mechanical behavior of alloys with influence of grain size distribution on the in a wide range of strain rates. Constitutive model was proposed for describing the inelastic deformation and damage of alloys with face centered cubic and hexagonal close packed structures and distribution of grain sizes. It was shown that the dependences of the yield stress on logarithm of normalized strain rate for aluminium and magnesium alloys with a bimodal distribution of grains and coarse-grained alloys are similar. The yield stress at room temperature of the magnesium and aluminium alloy increased on 10 - 15 % in comparison with a coarse-grained alloy if the volume fracture of the UFG grains is close to the percolation threshold.

  • 148.
    Shulumba, Nina
    et al.
    CALTECH, CA 91125 USA.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. CALTECH, CA 91125 USA.
    Minnich, Austin J.
    CALTECH, CA 91125 USA.
    Intrinsic localized mode and low thermal conductivity of PbSe2017In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 95, no 1, article id 014302Article in journal (Refereed)
    Abstract [en]

    Lead chalcogenides such as PbS, PbSe, and PbTe are of interest for their exceptional thermoelectric properties and strongly anharmonic lattice dynamics. Although PbTe has received the most attention, PbSe has a lower thermal conductivity and a nonlinear temperature dependence of thermal resistivity despite being stiffer, trends that prior first-principles calculations have not fully reproduced. Here, we use ab initio calculations that explicitly account for strong anharmonicity and a computationally efficient stochastic phase-space sampling scheme to identify the origin of this low thermal conductivity as an anomalously large anharmonic interaction, exceeding in strength that in PbTe, between the transverse optic and longitudinal acoustic branches. The strong anharmonicity is reflected in the striking observation of an intrinsic localized mode that forms in the acoustic frequencies. Our work shows the deep insights into thermal phonons that can be obtained from ab initio calculations that do not rely on perturbations from the ground-state phonon dispersion.

  • 149.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Investigation of vacancy-ordered Mo1.33C MXene from first principles and x-ray photoelectron spectroscopy2017In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 1, no 4, article id 044002Article in journal (Refereed)
    Abstract [en]

    MXenes are a comparatively young class of 2D materials, composed of transition-metal carbides/nitrides of the general formula Mn+1XnTx, where T represents surface terminations, typically O, OH, and/or F. Recently, a new type of MXene with vacancy ordering was discovered, Mo1.33CTx, with conduction and capacitance superior to the MXene counterpart without vacancies, Mo2CTx. We here present a theoretical evaluation of Mo1.33CTx based on first-principles calculations, where x = 2 and T is O, F, OH, or a mixture thereof. In addition to structural evaluation upon vacancy formation, we identify preferred terminations as well as termination sites, and resulting dynamical stability and electronic properties. For mixed terminations, the mixing energy is evaluated. We show that while Mo2C is typically O terminated, mixed terminations with a high F content are suggested for Mo1.33CTx, which in turn gives the highest metallicity out of all the configurations investigated. In addition, the results indicate a strong tuning potential of the band gap through choice of terminations, with an electronic structure changing between insulating and metallic depending on termination(s) and their configuration. We also performed x-ray photoelectron spectroscopy to identify and quantify the terminating species on the MXene, as well as their respective binding energies. The experimental results are consistent with the theoretical analysis, and combined they suggest an explanation to the MXene chemistry as well as the reported high conductivity of Mo1.33CTx.