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  • 1.
    Vorotilo, S.
    et al.
    Natl Univ Sci and Technol MISIS, Russia.
    Sidnov, K.
    Natl Univ Sci and Technol MISIS, Russia; Russian Acad Sci, Russia.
    Mosyagin, I. Yu
    Natl Univ Sci and Technol MISIS, Russia.
    Khvan, A. V
    Natl Univ Sci and Technol MISIS, Russia.
    Levashov, E. A.
    Natl Univ Sci and Technol MISIS, Russia.
    Patsera, E. I
    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. Natl Univ Sci and Technol MISIS, Russia.
    Ab-initio modeling and experimental investigation of properties of ultra-high temperature solid solutions TaxZr1-xC2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 778, p. 480-486Article in journal (Refereed)
    Abstract [en]

    Due to their high melting temperature, high-temperature oxidation resistance and outstanding mechanical properties, TaxZr1-xC solid solutions are promising ultra-high temperature ceramics (UHTC). However, accelerated knowledge-based development of UHTCs solid solutions requires reliable data regarding the properties of the solution phases in the whole interval of concentrations. At present, there are contradictory reports regarding the existence of the miscibility gap in Ta-Zr-C system at temperatures below 900 degrees C. In this work, we carry out ab-initio calculations of the thermodynamic properties of TaxZr1-xC alloys and demonstrate that the solid solutions should not decompose into TaC and ZrC end member compounds. We synthesize single-phase samples of TaxZr1-xC with compositions x = 0.9, 0.8, 0.6, and 0.3 by self-propagating high-temperature synthesis (SHS) and anneal the samples for 40 h. We do not observe any sign of the decomposition of the solid solution during the annealing, corroborating the conclusions obtained by theoretical simulations. (C) 2018 Elsevier B.V. All rights reserved.

    The full text will be freely available from 2020-11-19 15:39
  • 2.
    Leonov, Ivan
    et al.
    Russian Acad Sci, Russia; Natl Univ Sci and Technol MISIS, Russia.
    Rozenberg, Gregory Kh
    Tel Aviv Univ, Israel.
    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.
    Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures2019In: NPJ COMPUTATIONAL MATERIALS, ISSN 2057-3960, Vol. 5, article id 90Article in journal (Refereed)
    Abstract [en]

    The archetypal 3d Mott insulator hematite, Fe2O3, is one of the basic oxide components playing an important role in mineralogy of Earths lower mantle. Its high pressure-temperature behavior, such as the electronic properties, equation of state, and phase stability is of fundamental importance for understanding the properties and evolution of the Earths interior. Here, we study the electronic structure, magnetic state, and lattice stability of Fe2O3 at ultra-high pressures using the density functional plus dynamical mean-field theory (DFT + DMFT) approach. In the vicinity of a Mott transition, Fe2O3 is found to exhibit a series of complex electronic, magnetic, and structural transformations. In particular, it makes a phase transition to a metal with a post-perovskite crystal structure and site-selective local moments upon compression above 75 GPa. We show that the site-selective phase transition is accompanied by a charge disproportionation of Fe ions, with Fe-3 +/-delta and delta similar to 0.05-0.09, implying a complex interplay between electronic correlations and the lattice. Our results suggest that site-selective local moments in Fe2O3 persist up to ultra-high pressures of similar to 200-250 GPa, i.e., sufficiently above the core-mantle boundary. The latter can have important consequences for understanding of the velocity and density anomalies in the Earths lower mantle.

  • 3.
    Tal, Alexey A.
    et al.
    Ecole Polytech Fed Lausanne, Switzerland.
    Posada-Borbon, Alvaro
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Gronbeck, Henrik J.
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    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.
    Correlation between Ethylene Adsorption Energies and Core-Level Shifts for Pd Nanoclusters2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 4, p. 2544-2548Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations have been used to investigate the adsorption of ethylene on Pd nanoclusters together with shifts in core-level binding energies of Pd atoms bonded to the adsorbate. The adsorption energy is found to correlate with the core-level shifts (CLS), which is consistent with the notion that the core-level binding energy is a measure of differences in cohesion. The correlation between adsorption energies and core-level shifts is found to be stronger than the correlation between adsorption energies and generalized coordination numbers, indicating that descriptors preferably should account for electronic effects explicitly. The advantages of CLS as a descriptor for the screening of adsorption properties is discussed.

    The full text will be freely available from 2019-12-24 10:57
  • 4.
    Laniel, Dominique
    et al.
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Ponomareva, Alena V.
    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.
    Glazyrin, Konstantin
    DESY, Germany.
    Svitlyk, Volodymyr
    European Synchrotron Radiat Facil, France.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    High Pressure Investigation of the S-N-2 System up to the Megabar Range: Synthesis and Characterization of the SN2 Solid2019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 14, p. 9195-9204Article in journal (Refereed)
    Abstract [en]

    Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions, however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur nitrogen compounds. Above 64 GPa, an orthorhombic (space group Pnnm) SN2 compound was synthesized and characterized by single-crystal and powder X-ray diffraction as well as Raman spectroscopy. It is shown to adopt a CaCl2-type structure hence it is isostructural, isomassic, and isoelectronic to CaCl2-type SiO2 comprised of SN6 octahedra. Complementary theoretical calculations were performed to provide further insight into the physicochemical properties of SN2, notably its equation of state, the bonding type between its constitutive elements, and its electronic density of states. This new solid is shown to be metastable down to about 20 GPa, after which it spontaneously decomposes into S and N-2. This investigation shows that despite the many metastable S N compounds existing at ambient conditions, none of them are formed by pressure.

  • 5.
    Bykov, Maxim
    et al.
    Univ Bayreuth, Germany.
    Chariton, Stella
    Univ Bayreuth, Germany.
    Fei, Hongzhan
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Ponomareva, Alena V
    Natl Univ Sci and Technol MISIS, Russia.
    Tasnadi, Ferenc
    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.
    Merle, Benoit
    Friedrich Alexander Univ Erlangen Nurnberg FAU, Germany.
    Feldners, Patrick
    Friedrich Alexander Univ Erlangen Nurnberg FAU, Germany.
    Vogel, Sebastian
    Univ Munich LMU, Germany.
    Schnick, Wolfgang
    Univ Munich LMU, Germany.
    Prakapenka, Vitali B.
    Univ Chicago, IL 60637 USA.
    Greenberg, Eran
    Univ Chicago, IL 60637 USA.
    Hanfland, Michael
    European Synchrotron Radiat Facil, France.
    Pakhomova, Anna
    DESY, Germany.
    Liermann, Hanns-Peter
    DESY, Germany.
    Katsura, Tomoo
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re-2(N-2)(N)(2) stable at ambient conditions2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2994Article in journal (Refereed)
    Abstract [en]

    High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K-0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re-2(N-2)(N)(2). Unlike known transition metals pernitrides Re-2(N-2)(N)(2) contains both pernitride N-2(4-) and discrete N3- anions, which explains its exceptional properties. Re-2(N-2)(N)(2) can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re-2(N-2)(N)(2) turned to be at a threshold for superhard materials.

  • 6.
    Davidsson, Joel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ivády, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    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.
    Identification of divacancy and silicon vacancy qubits in 6H-SiC2019In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 11, article id 112107Article in journal (Refereed)
    Abstract [en]

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

  • 7.
    Jönsson, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    van Smaalen, Sander
    Univ Bayreuth, Germany.
    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.
    Inverse pressure-induced Mott transition in TiPO42019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 24, article id 245132Article in journal (Refereed)
    Abstract [en]

    TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.

  • 8.
    Krasilnikov, O. M.
    et al.
    NUST MISIS, Russia.
    Lugovskoy, A. V
    NUST MISIS, Russia; Radboud Univ Nijmegen, Netherlands.
    Dikan, V
    NUST MISIS, Russia; CSIC, Spain.
    Belov, M. P.
    NUST MISIS, Russia.
    Vekilov, Yu Kh
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Nonlinear elasticity of epsilon -Fe: The pressure effect2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 18, article id 184101Article in journal (Refereed)
    Abstract [en]

    Description of elasticity of iron at the ultrahigh pressures is a challenging task for physics, with a potential strong impact on other branches of science. In the present work, we calculate the elastic properties of hcp iron in the pressure range of 50-340 GPa beyond the linear elasticity approximation, conventionally assumed in theoretical studies. We define the higher order elastic constants and present expressions for the long-wave acoustic modes Gruneisen parameters of a compressed hcp crystal. We obtain the second and third order elastic constants of the hcp Fe in the considered pressure interval, as well as its Gruneisen parameters for the high-symmetry directions. The latter are directly compared with the Gruneisen parameters derived from the volume dependences of the vibrational frequencies calculated in the quasiharmonic approximation. The obtained results are used for the stability analysis of the hcp phase of iron at high pressures.

  • 9.
    Pakhomova, Anna
    et al.
    DESY, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Gorelova, Liudmila
    St Petersburg State Univ, Russia.
    Krivovichev, Sergey S.
    St Petersburg State Univ, Russia; Russian Acad Sci, Russia.
    Belov, Maxim P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Penta- and hexa-coordinated beryllium and phosphorus in high-pressure modifications of CaBe2P2O82019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2800Article in journal (Refereed)
    Abstract [en]

    Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe2P2O8, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe2P2O8 is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.

  • 10.
    Monteseguro, V
    et al.
    Univ Valencia, Spain; European Radiat Synchrotron Facil, France.
    Sans, J. A.
    Univ Politecn Valencia, Spain.
    Cuartero, V
    European Radiat Synchrotron Facil, France; Ctr Univ Def Zaragoza, Spain.
    Cova, F.
    European Radiat Synchrotron Facil, France.
    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.
    Olovsson, Weine
    Linköping University, National Supercomputer Centre (NSC). Linköping University, Faculty of Science & Engineering.
    Popescu, C.
    ALBA CELLS, Spain.
    Pascarelli, S.
    European Radiat Synchrotron Facil, France.
    Garbarino, G.
    European Radiat Synchrotron Facil, France.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Irifune, T.
    Ehime Univ, Japan; Tokyo Inst Technol, Japan.
    Errandonea, D.
    Univ Valencia, Spain.
    Phase stability and electronic structure of iridium metal at the megabar range2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8940Article in journal (Refereed)
    Abstract [en]

    The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.

  • 11.
    Mosyagin, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISTS, Russia.
    Lugovskoy, A. V.
    NUST MISTS, Russia.
    Krasilnikov, O. M.
    NUST MISTS, Russia; NUST MISTS, Russia.
    Vekilov, Yu. Kh.
    NUST MISTS, Russia; NUST MISTS, 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.
    Reply to the comment by M. Mazdziarz on the article "Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017) 20-30]2019In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 235, p. 295-296Article in journal (Other academic)
    Abstract [en]

    Marcin Mazdziarz has published a comment on our recent paper by I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, Yu.Kh. Vekilov, S.I. Simak and L.A. Abrikosov titled "Ab initio calculations of pressure dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017)2030]. The author states that there are serious fundamental errors and flaws. In this reply we clarify all misunderstanding mentioned in the said comment. (C) 2018 Published by Elsevier B.V.

    The full text will be freely available from 2020-06-19 15:55
  • 12.
    Sangiovanni, Davide
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Smirnova, D.
    Ruhr Univ Bochum, Germany; Russian Acad Sci, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gambino, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Mrovec, M.
    Ruhr Univ Bochum, Germany.
    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.
    Superioniclike Diffusion in an Elemental Crystal: bcc Titanium2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 10, article id 105501Article in journal (Refereed)
    Abstract [en]

    Recent theoretical investigations [A. B. Belonoshko et aL Nat. Geosci. 10, 312 (2017)] revealed the occurrence of the concerted migration of several atoms in bcc Fe at inner-core temperatures and pressures. Here, we combine first-principles and semiempirical atomistic simulations to show that a diffusion mechanism analogous to the one predicted for bcc iron at extreme conditions is also operative and of relevance for the high-temperature bcc phase of pure Ti at ambient pressure. The mechanism entails a rapid collective movement of numerous (from two to dozens) neighbors along tangled closed-loop paths in defect-free crystal regions. We argue that this phenomenon closely resembles the diffusion behavior of superionics and liquid metals. Furthermore, we suggest that concerted migration is the atomistic manifestation of vanishingly small co-mode phonon frequencies previously detected via neutron scattering and the mechanism underlying anomalously large and markedly non-Arrhenius self-diffusivities characteristic of bcc Ti.

  • 13.
    Palonen, H.
    et al.
    Uppsala Univ, Sweden.
    Mukhamedov, B. O.
    Natl Univ Sci and Technol MISIS, Russia.
    Ponomareva, A. V.
    Natl Univ Sci and Technol MISIS, Russia.
    Palsson, G. K.
    Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hjorvarsson, B.
    Uppsala Univ, Sweden.
    The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice2019In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, no 1, article id 012406Article in journal (Refereed)
    Abstract [en]

    The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing.

  • 14.
    Ning, Weihua
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Tech Univ, Peoples R China.
    Zhao, Xin-Gang
    Jilin Univ, Peoples R China.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bai, Sai
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ji, Fuxiang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tao, Youtian
    Nanjing Tech Univ, Peoples R China.
    Ren, Xiao-Ming
    Nanjing Tech Univ, Peoples R China.
    Zhang, Lijun
    Jilin Univ, Peoples R China.
    Huang, Wei
    Nanjing Tech Univ, Peoples R China.
    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.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Thermochromic Lead-Free Halide Double Perovskites2019In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 10, article id 1807375Article in journal (Refereed)
    Abstract [en]

    Lead-free halide double perovskites with diverse electronic structures and optical responses, as well as superior material stability show great promise for a range of optoelectronic applications. However, their large bandgaps limit their applications in the visible light range such as solar cells. In this work, an efficient temperature-derived bandgap modulation, that is, an exotic fully reversible thermochromism in both single crystals and thin films of Cs2AgBiBr6 double perovskites is demonstrated. Along with the thermochromism, temperature-dependent changes in the bond lengths of Ag Symbol of the Klingon Empire Br (R-Ag Symbol of the Klingon Empire Br) and Bi Symbol of the Klingon Empire Br (R-Bi Symbol of the Klingon Empire Br) are observed. The first-principle molecular dynamics simulations reveal substantial anharmonic fluctuations of the R-Ag Symbol of the Klingon Empire Br and R-Bi Symbol of the Klingon Empire Br at high temperatures. The synergy of anharmonic fluctuations and associated electron-phonon coupling, and the peculiar spin-orbit coupling effect, is responsible for the thermochromism. In addition, the intrinsic bandgap of Cs2AgBiBr6 shows negligible changes after repeated heating/cooling cycles under ambient conditions, indicating excellent thermal and environmental stability. This work demonstrates a stable thermochromic lead-free double perovskite that has great potential in the applications of smart windows and temperature sensors. Moreover, the findings on the structure modulation-induced bandgap narrowing of Cs2AgBiBr6 provide new insights for the further development of optoelectronic devices based on the lead-free halide double perovskites.

    The full text will be freely available from 2020-01-20 15:10
  • 15.
    Mukhamedov, B. O.
    et al.
    Natl Univ Sci and Technol MISIS, Russia.
    Saenko, I
    Freiberg Univ Min and Technol, Germany; Russian Acad Sci, Russia.
    Ponomareva, A. V
    Natl Univ Sci and Technol MISIS, Russia.
    Kriegel, M. J.
    Freiberg Univ Min and Technol, Germany.
    Chugreev, A.
    Leibniz Univ Hannover, Germany.
    Udovsky, A.
    Russian Acad Sci, Russia; Natl Res Nucl Univ MEPhl, Russia.
    Fabrichnaya, O.
    Freiberg Univ Min and Technol, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Thermodynamic and physical properties of Zr3Fe and ZrFe2 intermetallic compounds2019In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 109, p. 189-196Article in journal (Refereed)
    Abstract [en]

    Experimental differential scanning calorimetry measurements and ab-initio simulations were carried out to define the heat capacities of Zr3Fe and C15-ZrFe2 compounds from 0 K up to their maximum stability temperatures. Experimental measurements of heat capacity of each compound were performed for the first time in wide range of temperatures. Density functional theory and quasi-harmonic approximation (QHA) were employed to calculate the free energy of the studied systems as a function of volume and temperature. A good agreement was observed between theoretical and experimental heat capacities within validity range of the QHA. This makes it possible to combine theoretical and experimental data to determine the standard entropies of intermetallic compounds.

    The full text will be freely available from 2021-04-03 08:54
  • 16.
    Khvan, A. V.
    et al.
    NUST MISIS, Russia.
    Babkina, T.
    Lomonosov Moscow State Univ, Russia.
    Dinsdale, A. T.
    Hampton Thermodynam Ltd, England.
    Uspenskaya, I. A.
    Lomonosov Moscow State Univ, Russia.
    Fartushna, I. V.
    NUST MISIS, Russia.
    Druzhinina, A. I.
    Lomonosov Moscow State Univ, Russia.
    Syzdykova, A. B.
    NUST MISIS, Russia.
    Belov, M. P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Thermodynamic properties of tin: Part I Experimental investigation, ab-initio modelling of alpha-, beta-phase and a thermodynamic description for pure metal in solid and liquid state from 0 K2019In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 65, p. 50-72Article in journal (Refereed)
    Abstract [en]

    Thermodynamic data for crystalline white and grey tin were assessed using an extended Einstein model from 0 K. Ab-initio simulations in the framework of density functional theory (DFT) with the quasiharmonic approximation (QHA) were carried out to define the heat capacities for both phases of tin from 0 K up to room temperatures. Good agreement was observed between theoretical and experimental heat capacities, which makes it possible to combine theoretical and experimental data to determine the standard entropies. Data for the liquid phase were described using a two state model. During the assessment, careful analysis of the experimental data was carried out. In order to fulfil the need for a precise evaluation of S-298(o) we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point and to estimate solid phase transition entropy and enthalpy which are difficult to measure due to a high activation barrier. Additional measurements of heat capacity were carried out where existing data were scarce.

    The full text will be freely available from 2021-02-16 11:17
  • 17.
    Skripnyak, Natalia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ponomareva, A. V.
    Natl Univ Sci and Technol MISIS, Russia.
    Belov, M. P.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ab initio calculations of elastic properties of alloys with mechanical instability: Application to BCC Ti-V alloys2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 140, p. 357-365Article in journal (Refereed)
    Abstract [en]

    Considering Ti-V alloys with the body-centered cubic crystal lattice, a system with mechanical instability for Tirich alloys, we calculate their elastic properties using Projector Augmented Wave method and the exact muffin tin orbital method in a complete interval of V concentrations. The substitutional disorder is modeled using the special quasi-random structures technique and the coherent potential approximation. The efficiency and accuracy of the simulation techniques is analyzed, and a strategy for efficient high-throughput calculations of elastic properties of disordered alloys is proposed. Dependences of the single crystal elastic moduli on V concentration and a set ofmechanical characteristics of polycrystalline alloys are presented and discussed. The effect of V content on themechanical stabilization of the bcc Ti-V alloys is investigated. In agreement with experiment, we find that titanium-rich alloys are mechanically unstable, however the alloys becomemechanically stablewith increasing content of V in the system. We observe a nonlinear dependence of the alloys Youngs moduli in a vicinity of the mechanical stabilization and suggest that this effect can be used to design alloys with low values of the elastic moduli. (C) 2017 Elsevier Ltd. All rights reserved.

  • 18.
    Ekholm, Marcus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gambino, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    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.
    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.
    Assessing the SCAN functional for itinerant electron ferromagnets2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 9, article id 094413Article in journal (Refereed)
    Abstract [en]

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

  • 19.
    Eriksson, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Tal, Alexey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Skallberg, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Brommesson, Caroline
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Hu, Zhang-Jun
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Boyd, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Fairley, Neal
    Casa Software Ltd, Bay House, Teignmouth, United Kingdom.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Materials Modeling and Development Laboratory, National University of Science and Technology “MISIS”, Moscow, Russia.
    Zhang, Xuanjun
    Faculty of Health Sciences, University of Macau, Macau, SAR, China.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Cerium oxide nanoparticles with antioxidant capabilities and gadolinium integration for MRI contrast enhancement2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6999Article in journal (Refereed)
    Abstract [en]

    The chelating gadolinium-complex is routinely used as magnetic resonance imaging (MRI) -contrast enhancer. However, several safety issues have recently been reported by FDA and PRAC. There is an urgent need for the next generation of safer MRI-contrast enhancers, with improved local contrast and targeting capabilities. Cerium oxide nanoparticles (CeNPs) are designed with fractions of up to 50% gadolinium to utilize the superior MRI-contrast properties of gadolinium. CeNPs are well-tolerated in vivo and have redox properties making them suitable for biomedical applications, for example scavenging purposes on the tissue-and cellular level and during tumor treatment to reduce in vivo inflammatory processes. Our near edge X-ray absorption fine structure (NEXAFS) studies show that implementation of gadolinium changes the initial co-existence of oxidation states Ce3+ and Ce4+ of cerium, thereby affecting the scavenging properties of the nanoparticles. Based on ab initio electronic structure calculations, we describe the most prominent spectral features for the respective oxidation states. The as-prepared gadolinium-implemented CeNPs are 3-5 nm in size, have r(1)-relaxivities between 7-13 mM(-1) s(-1) and show clear antioxidative properties, all of which means they are promising theranostic agents for use in future biomedical applications.

  • 20.
    Pourovskii, L. V.
    et al.
    Univ Paris Saclay, France; Coll France, France; Natl Univ Sci and Technol MISIS, Russia.
    Mravlje, J.
    Jozef Stefan Inst, Slovenia.
    Georges, A.
    Univ Paris Saclay, France; Coll France, France; Univ 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. Natl Univ Sci and Technol MISIS, Russia.
    Correction: Electron-electron scattering and thermal conductivity of epsilon-iron at Earths core conditions (vol 19, 073022, 2017)2018In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 109501Article in journal (Refereed)
    Abstract [en]

    n/a

  • 21.
    Mosyagin, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Gambino, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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 Univ Bochum, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Caffrey, Nuala M.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Trinity Coll Dublin, Ireland.
    Effect of dispersion corrections on ab initio predictions of graphite and diamond properties under pressure2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 17, article id 174103Article in journal (Refereed)
    Abstract [en]

    There are several approaches to the description of van der Waals (vdW) forces within density functional theory. While they are generally found to improve the structural and energetic properties of those materials dominated by weak dispersion forces, it is not known how they behave when the material is subject to an external pressure. This could be an issue when considering the pressure-induced structural phase transitions, which are currently attracting great attention following the discovery of an ultrahard phase formed by the compression of graphite at room temperature. In order to model this transition, the functional must be capable of simultaneously describing both strong covalent bonds and weak dispersion interactions as an isotropic pressure is applied. Here, we report on the ability of several dispersion-correction functionals to describe the energetic, structural, and elastic properties of graphite and diamond, when subjected to an isotropic pressure. Almost all of the tested vdW corrections provide an improved description of both graphite and diamond compared to the local density approximation. The relative error does not change significantly as pressure is applied, and in some cases even decreases. We therefore conclude that the use of dispersion-corrected exchange-correlation functionals, which have been neglected to date, will improve the accuracy and reliability of theoretical investigations into the pressure-induced phase transition of graphite.

  • 22.
    Ponomareva, A. V.
    et al.
    Natl Univ Sci and Technol MISIS, Russia.
    Ruban, A. V.
    KTH Royal Inst Technol, Sweden; Leoben Forsch GmbH, Austria.
    Mukhamedov, B. O.
    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.
    Effect of multicomponent alloying with Ni, Mn and Mo on phase stability of bcc Fe-Cr alloys2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 150, p. 117-129Article in journal (Refereed)
    Abstract [en]

    Fe-Cr system attracts lot of attention in condensed matter physics due to its technological importance and extraordinary physics related to a non-trivial interplay between magnetic and chemical interactions. However, the effect of multicomponent alloying on the properties of Fe-Cr alloys are less studied. We have calculated the mixing enthalpy, magnetic moments, effective chemical, strain-induced and magnetic exchange interactions to investigate the alloying effect of Ni, Mn, Mo on the phase stability of the ferromagnetic bcc Fe Cr system at zero K. We demonstrate that the alloying reduces the stability of Fe-Cr alloys and expands the region of spinodal decomposition. At the same time, the mixing enthalpy in ternary Fe100-c-05CrcNi05 alloys indicates a stability of solid solution phase up to 6 at. % Cr. In Fem(100-c-07)CrNi(05)Mn(01)Mo(01) alloys, we did not find any alloy composition that has negative enthalpy of formation. Analyzing magnetic and electronic properties of the alloys and investigating magnetic, chemical and strain-induced interactions in the studied systems, we provide physically transparent picture of the main factors leading to the destabilization of the Fe-Cr solid solutions by the multicomponent alloying with Ni, Mn, Mo. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    The full text will be freely available from 2020-03-15 13:27
  • 23.
    Mozafari, Elham
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. 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.
    Belov, Maxim P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Effect of the lattice dynamics on the electronic structure of paramagnetic NiO within the disordered local moment picture2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 3, article id 035152Article in journal (Refereed)
    Abstract [en]

    Using the disordered local moments approach in combination with the ab initio molecular dynamics method, we simulate the behavior of a paramagnetic phase of NiO at finite temperatures to investigate the effect of magnetic disorder, thermal expansion, and lattice vibrations on its electronic structure. In addition, we study its lattice dynamics. We verify the reliability of our theoretical scheme via comparison of our results with available experiment and earlier theoretical studies carried out within static approximations. We present the phonon dispersion relations for the paramagnetic rock-salt (B1) phase of NiO and demonstrate that it is dynamically stable. We observe that including the magnetic disorder to simulate the paramagnetic phase has a small yet visible effect on the band gap. The amplitude of the local magnetic moment of Ni ions from our calculations for both antiferromagnetic and paramagnetic phases agree well with other theoretical and experimental values. We demonstrate that the increase of temperature up to 1000 K does not affect the electronic structure strongly. Taking into account the lattice vibrations and thermal expansion at higher temperatures have amajor impact on the electronic structure, reducing the band gap from similar to 3.5 eV at 600 K to similar to 2.5 eV at 2000 K. We conclude that static lattice approximations can be safely employed in simulations of the paramagnetic state of NiO up to relatively high temperatures (similar to 1000 K), but as we get closer to the melting temperature vibrational effects become quite large and therefore should be included in the calculations.

  • 24.
    Xia, Chao
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Tal, Alexey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Johansson, Leif
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Linköping University, National Supercomputer Centre (NSC).
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Effects of rhenium on graphene grown on SiC(0001)2018In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 222, p. 117-121Article in journal (Refereed)
    Abstract [en]

    We study the effects of Rhenium (Re) deposited on epitaxial monolayer graphene grown on SiC(0001) and after subsequent annealing at different temperatures, by performing high resolution photoelectron spectroscopy (PES) and angle resolved photoelectron spectroscopy (ARPES). The graphene-Re system is found to be thermally stable. While no intercalation or chemical reaction of the Re is detected after deposition and subsequent annealing up to 1200 degrees C, a gradual decrease in the binding energy of the Re 4f doublet is observed. We propose that a larger mobility of the Re atoms with increasing annealing temperature and hopping of Re atoms between different defective sites on the graphene sample could induce this decrease of Re 4f binding energy. This is corroborated by first principles density functional theory (DFT) calculations of the Re core-level binding energy shift. No change in the doping or splitting of the initial monolayer graphene electronic band structure is observed after Re deposition and annealing up to 1200 degrees C, only a broadening of the bands. (C) 2017 Elsevier B.V. All rights reserved.

  • 25.
    Bykov, M.
    et al.
    Univ Bayreuth, Germany.
    Bykova, E.
    Univ Bayreuth, Germany; DESY, Germany.
    Aprilis, G.
    Univ Bayreuth, Germany.
    Glazyrin, K.
    DESY, Germany.
    Koemets, E.
    Univ Bayreuth, Germany.
    Chuvashova, I
    Univ Bayreuth, Germany; Univ Bayreuth, Germany.
    Kupenko, I
    Univ Munster, Germany.
    McCammon, C.
    Univ Bayreuth, Germany.
    Mezouar, M.
    European Synchrotron Radiat Facil, France.
    Prakapenka, V
    Univ Chicago, IL 60437 USA.
    Liermann, H-P
    DESY, Germany.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Ponomareva, A. V
    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.
    Dubrovinskaia, N.
    Univ Bayreuth, Germany.
    Dubrovinsky, L.
    Univ Bayreuth, Germany.
    Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 2756Article in journal (Refereed)
    Abstract [en]

    Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N-N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure. Here, through a direct reaction between Fe and N-2 in a laser-heated diamond anvil cell, we synthesize three ironnitrogen compounds Fe3N2, FeN2 and FeN4. Their crystal structures are revealed by single-crystal synchrotron X-ray diffraction. Fe3N2, synthesized at 50 GPa, is isostructural to chromium carbide Cr3C2. FeN2 has a marcasite structure type and features covalently bonded dinitrogen units in its crystal structure. FeN4, synthesized at 106 GPa, features polymeric nitrogen chains of [N-4(2-)](n) units. Based on results of structural studies and theoretical analysis, [N-4(2-)](n) units in this compound reveal catena-poly[tetraz-1-ene-1,4-diyl] anions.

  • 26.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Acad Sci, Hungary.
    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.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    First principles calculation of spin-related quantities for point defect qubit research2018In: NPJ COMPUTATIONAL MATERIALS, ISSN 2057-3960, Vol. 4, article id 76Article, review/survey (Refereed)
    Abstract [en]

    Point defect research in semiconductors has gained remarkable new momentum due to the identification of special point defects that can implement qubits and single photon emitters with unique characteristics. Indeed, these implementations are among the few alternatives for quantum technologies that may operate even at room temperature, and therefore discoveries and characterization of novel point defects may highly facilitate future solid state quantum technologies. First principles calculations play an important role in point defect research, since they provide a direct, extended insight into the formation of the defect states. In the last decades, considerable efforts have been made to calculate spin-dependent properties of point defects from first principles. The developed methods have already demonstrated their essential role in quantitative understanding of the physics and application of point defect qubits. Here, we review and discuss accuracy aspects of these novel ab initio methods and report on their most relevant applications for existing point defect qubits in semiconductors. We pay attention to the advantages and limitations of the methodological solutions and highlight additional developments that are expected in the near future. Moreover, we discuss the opportunity of a systematic search for potential point defect qubits, as well as the possible development of predictive spin dynamic simulations facilitated by ab initio calculations of spin-dependent quantities.

  • 27.
    Davidsson, Joel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ivády, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    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.
    First principles predictions of magneto-optical data for semiconductor point defect identification: the case of divacancy defects in 4H-SiC2018In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 023035Article in journal (Refereed)
    Abstract [en]

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

  • 28.
    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.
    Rogström, Lina
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Zhu, Jianqiang
    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.
    Hsu, Tun-Wei
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Lind, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film 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. Natl Univ Sci and Technol MISIS, Russia.
    Johansson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    High temperature thermodynamics of spinodal decomposition in arc deposited TixNbyAlzN coatings2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 150, p. 165-170Article in journal (Refereed)
    Abstract [en]

    Using first principles calculations and experimental methods we show that B1 structured solid solution TixNbyAlzN can be grown. The mixing free energy surface indicates that the alloys should decompose. Theoretical analysis of the thermodynamic driving force towards the spinodal decomposition shows that the force can be different in alloys with equally low thermodynamic stability but different Nb content, indicating that the detailed picture of the decomposition should also be different. Electron microscopy and nanoindentation underlines different age hardening of the samples. We demonstrate that an alloy with the optimized composition, Ti0.42Nb0.17Al0.41N combines high thermal stability and age hardening behavior.

  • 29.
    Bykov, Maxim
    et al.
    Univ Bayreuth, Germany.
    Bykova, Elena
    Deutsch Elektronen Synchrotron DESY, Germany.
    Koemets, Egor
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Glazyrin, Konstantin
    Deutsch Elektronen Synchrotron DESY, Germany.
    Liermann, Hanns-Peter
    Deutsch Elektronen Synchrotron DESY, Germany.
    Ponomareva, Alena V.
    Natl Univ Sci and Technol MISIS, Russia.
    Tidholm, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    High-Pressure Synthesis of a Nitrogen-Rich Inclusion Compound ReN8·xN2 with Conjugated Polymeric Nitrogen Chains2018In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 57, no 29, p. 9048-9053Article in journal (Refereed)
    Abstract [en]

    A nitrogen-rich compound, ReN(8)xN(2), was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN8 framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100GPa, ReN(8)xN(2) is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [-N=N-] that constitute the framework have not been previously observed in any compound. Abinitio calculations on ReN(8)xN(2) provide strong support for the experimental results and conclusions.

  • 30.
    Bykova, E.
    et al.
    DESY, Germany; Univ Bayreuth, Germany.
    Bykov, M.
    Univ Bayreuth, Germany; Natl Univ Sci and Technol MISIS, Russia.
    Cernok, A.
    Univ Bayreuth, Germany; Open Univ, England.
    Tidholm, 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.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. CALTECH, CA 91125 USA.
    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.
    Liermann, H. -P.
    DESY, Germany.
    Hanfland, M.
    European Synchrotron Radiat Facil, France.
    Prakapenka, V. B.
    Univ Chicago, IL 60637 USA.
    Prescher, C.
    Univ Chicago, IL 60637 USA; Univ Cologne, Germany.
    Dubrovinskaia, N.
    Univ Bayreuth, Germany.
    Dubrovinsky, L.
    Univ Bayreuth, Germany.
    Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 4789Article in journal (Refereed)
    Abstract [en]

    Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge of the local structures of silicates and silica (SiO2) melts at deep mantle conditions and of their densification mechanisms is still limited. Here we report the synthesis and characterization of metastable high-pressure silica phases, coesite-IV and coesite-V, using in situ single-crystal X-ray diffraction and ab initio simulations. Their crystal structures are drastically different from any previously considered models, but explain well features of pair-distribution functions of highly densified silica glass and molten basalt at high pressure. Built of four, five-, and six-coordinated silicon, coesite-IV and coesite-V contain SiO6 octahedra, which, at odds with 3rd Paulings rule, are connected through common faces. Our results suggest that possible silicate liquids in Earths lower mantle may have complex structures making them more compressible than previously supposed.

  • 31.
    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.

  • 32.
    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.

  • 33.
    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.

  • 34.
    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.

  • 35.
    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.

  • 36.
    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.

  • 37.
    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.

  • 38.
    Golosova, N. O.
    et al.
    Joint Institute Nucl Research, Russia.
    Kozlenko, D. P.
    Joint Institute Nucl Research, Russia.
    Dubrovinsky, L. S.
    University of Bayreuth, Germany.
    Cerantola, V.
    European Synchrotron Radiat Facil, France.
    Bykov, M.
    University of Bayreuth, Germany.
    Bykova, E.
    University of Bayreuth, Germany; DESY, Germany.
    Kichanov, S. E.
    Joint Institute Nucl Research, Russia.
    Lukin, E. V.
    Joint Institute Nucl Research, Russia.
    Savenko, B. N.
    Joint Institute Nucl Research, Russia.
    Ponomareva, A. V.
    National University of Science and Technology MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Magnetic and structural properties of FeCO3 at high pressures2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 13, article id 134405Article in journal (Refereed)
    Abstract [en]

    The structural and magnetic properties of siderite FeCO3 have been studied by means of neutron powder diffraction at pressures up to 7.5 GPa and first-principles theoretical calculations. The lattice compression in the rhombohedral calcite-type structure is dominated by the reduction of the Fe-O bonds, while the changes of the C-O bonds are much less pronounced. The Neel temperature of the antiferromagnetic ( AFM) ground state increases substantially under pressure with a coefficient dT(N)/dP = 1.8K/GPa, which is about 1.5 times larger in comparison with those predicted by the empirical Bloch rule. The ab initio calculations were performed in the framework of the density functional theory including Hubbard-U correction. The calculated structural parameters and Neel temperature as functions of pressure provide a reasonable agreement with the experimental results. The analysis of the density of electronic states points toward increased covalent bonding between the Fe and O atoms upon pressure, giving rise to unexpectedly large pressure coefficient of the Neel temperature and reduced ordered magnetic moments of Fe atoms.

  • 39.
    Leonov, I.
    et al.
    University of Augsburg, Germany; National University of Science and Technology MISIS, Russia.
    Greenberg, E.
    Tel Aviv University, Israel; University of Chicago, IL USA.
    Belov, M. P.
    National University of Science and Technology MISIS, Russia.
    Rozenberg, G. Kh.
    Tel Aviv University, Israel.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Mott transition and magnetic collapse in iron-bearing compounds under high pressure2017In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 37, no 2, p. 96-118Article in journal (Refereed)
    Abstract [en]

    We discuss the electronic, magnetic, and related structural transitions in the iron-based Mott insulators under high pressures relevant to the Earths lower mantle conditions. The paper focuses on the above-mentioned topics based primarily on our theoretical analysis and various experimental studies employing synchrotron X-ray diffraction, Fe-57 Mossbauer spectroscopy, and electrical transport measurements. We review the main theoretical tools employed for the analysis of the properties of materials with strongly interacting electrons and discuss the problems of theoretical description of such systems. In particular, we discuss a state-of-the-art method for calculating the electronic structure of strongly correlated materials, the DFT + DMFT method, which merges standard band-structure techniques (DFT) with dynamical mean-field theory of correlated electrons (DMFT). We employ this method to study the pressure-induced magnetic collapse in Mott insulators, such as wustite (FeO), magnesiowustite (Fe1-xMgx)O (x=0.25 and 0.75) and goethite (FeOOH), and explore the consequences of the magnetic collapse for the electronic structure and phase stability of these materials. We show that the paramagnetic cubic B1-structured FeO and (Fe,Mg)O and distorted orthorhombic (Pnma) FeOOH exhibit upon compression a high-to low-spin (HS-LS) transition, which is accompanied by a simultaneous collapse of local moments. However, the HS-LS transition is found to have different consequences for the electronic properties of these compounds. For FeO and (Fe0.75Mg0.25)O, the transition is found to be accompanied by a Mott insulator-to-metal phase transition. In contrast to that, both (Fe0.25Mg0.75)O and FeOOH remain insulating up to the highest studied pressures, indicating that a Mott insulator to band insulator phase transition takes place. Our combined theoretical and experimental studies indicate a crossover between localized to itinerant moment behavior to accompany magnetic collapse of Fe ions.

  • 40.
    Gambino, Davide
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
    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.
    Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 10, article id 104306Article in journal (Refereed)
    Abstract [en]

    We use the color diffusion (CD) algorithm in nonequilibrium (accelerated) ab initio molecular dynamics simulations to determine Ti monovacancy jump frequencies in NaCl-structure titanium nitride (TiN), at temperatures ranging from 2200 to 3000 K. Our results showthat theCDmethod extended beyond the linear-fitting rate-versus-force regime [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)] can efficiently determine metal vacancy migration rates in TiN, despite the low mobilities of lattice defects in this type of ceramic compound. We propose a computational method based on gamma-distribution statistics, which provides unambiguous definition of nonequilibrium and equilibrium (extrapolated) vacancy jump rates with corresponding statistical uncertainties. The acceleration-factor achieved in our implementation of nonequilibrium molecular dynamics increases dramatically for decreasing temperatures from 500 for T close to the melting point T-m, up to 33 000 for T approximate to 0.7 T-m

  • 41.
    Tasnadi, Ferenc
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Lugovskoy, Andrey V.
    NUST MISIS, Russia.
    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. NUST MISIS, Russia.
    Non-equilibrium vacancy formation energies in metastable alloys - A case study of Ti0.5Al0.5N2017In: MATERIALS and DESIGN, ISSN 0264-1275, Vol. 114, p. 484-493Article in journal (Refereed)
    Abstract [en]

    In this study, we present a computational technique to investigate non-equilibrium vacancies in metastable alloys. In contrast to equilibrium materials, calculation of the energy of removing an alloying atom requires a finite size configurational correction. We explain that in metastable alloys the vacancy formation energy is defined up to an arbitrary constant. We argue that in non-equilibrium alloys no statistical considerations are required and there is a distribution of the vacancy formation energy with large variation. We show for the example of Ti0.5Al0.5N that the configuration correction is significant. Using cluster expansion, we demonstrate the major importance of the first two metallic coordination shells in Ti0.5Al0.5N. We introduce a three-dimensional representation of the energies of removing Ti and Al atoms as a function of number of Al atoms in the neighboring shells and we predict the metal atom vacancy formation energy in arbitrary local chemical environments. Neglecting the interactions between the vacant sites and assuming their simultaneous occurrence, we show how to extract information about the energy cost of a vacancy concentration in metastable alloys. We conclude that in metastable disordered alloys vacancies should occur in local environments that correspond to the lowest formation energies rather than distributed statistically. (C) 2016 Elsevier Ltd. All rights reserved.

  • 42.
    Shtepliuk, Ivan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NASU, Ukraine.
    Caffrey, Nuala M.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Trinity Coll Dublin, Ireland; Trinity Coll Dublin, Ireland.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Khranovskyy, Volodymyr
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor 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. National University of Science and Technology MISIS, Russia.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    On the interaction of toxic Heavy Metals (Cd, Hg, Pb) with graphene quantum dots and infinite graphene2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 3934Article in journal (Refereed)
    Abstract [en]

    The promise of graphene and its derivatives as next generation sensors for real-time detection of toxic heavy metals (HM) requires a clear understanding of behavior of these metals on the graphene surface and response of the graphene to adsorption events. Our calculations herein were focused on the investigation of the interaction between three HMs, namely Cd, Hg and Pb, with graphene quantum dots (GQDs). We determine binding energies and heights of both neutral and charged HM ions on these GQDs. The results show that the adsorption energy of donor-like physisorbed neutral Pb atoms is larger than that of either Cd or Hg. In contrast to the donor-like behavior of elemental HMs, the chemisorbed charged HM species act as typical acceptors. The energy barriers to migration of the neutral adatoms on GQDs are also estimated. In addition, we show how the substitution of a carbon atom by a HM adatom changes the geometric structure of GQDs and hence their electronic and vibrational properties. UV-visible absorption spectra of HM-adsorbed GQDs vary with the size and shape of the GQD. Based on our results, we suggest a route towards the development of a graphene-based sensing platform for the optical detection of toxic HMs.

  • 43.
    Tal, Alexey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Origin of the core-level binding energy shifts in Au nanoclusters2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 24, article id 245402Article in journal (Refereed)
    Abstract [en]

    We investigate the shifts of the core-level binding energies in small gold nanoclusters by using ab initio density-functional-theory calculations. The shift of the 4f states is calculated for magic-number nanoclusters in a wide range of sizes and morphologies. We find a nonmonotonous behavior of the core-level shift in nanoclusters depending on the size. We demonstrate that there are three main contributions to the Au 4f shifts, which depend sensitively on the interatomic distances, coordination, and quantum confinement. They are identified and explained by the change of the on-site electrostatic potential.

  • 44.
    Leonov, I.
    et al.
    University of Augsburg, Germany; National University of Science and Technology MISIS, Russia.
    Ponomareva, A. V.
    National University of Science and Technology MISIS, Russia.
    Nazarov, R.
    Lawrence Livermore National Lab, CA 94551 USA.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Pressure-induced spin-state transition of iron in magnesiowustite (Fe,Mg)O2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075136Article in journal (Refereed)
    Abstract [en]

    We present a detailed theoretical study of the electronic, magnetic, and structural properties of magnesiowustite Fe-1 Mg-x(x) O with x in the range between 0 and 0.875 using a fully charge self-consistent implementation of the density functional theory plus dynamical mean-field theory method. In particular, we compute the electronic structure and phase stability of the rocksalt B1-structured (Fe,Mg) O at high pressures relevant for the Earths lower mantle. We find that upon compression paramagnetic (Fe,Mg) O exhibits a spin-state transition of Fe2+ ions from a high-spin to low-spin (HS-LS) state which is accompanied by a collapse of local magnetic moments. The HS-LS transition results in a substantial drop in the lattice volume by about 4%-8%, implying a complex interplay between electronic and lattice degrees of freedom. Our results reveal a strong sensitivity of the calculated transition pressure P-tr. upon addition of Mg. While, for Fe-rich magnesiowustite with Mg x amp;lt; 0.5, Ptr. is about 80 GPa, for Mg x = 0.75 it drops to 52 GPa, i. e., by 35%. This behavior is accompanied by a substantial change in the spin transition range from 50 to 140 GPa in FeO to 30 to 90 GPa for x = 0.75. In addition, the calculated bulk modulus (in the HS state) is found to increase by similar to 12% from 142 GPa in FeO to 159 GPa in (Fe,Mg) O with Mg x = 0.875. We find that the pressure-induced HS-LS transition has different consequences for the electronic properties of the Fe-rich and -poor (Fe,Mg) O. For the Fe-rich (Fe,Mg) O, the transition is found to be accompanied by a Mott insulator to a (semi) metal phase transition. In contrast to that, for x amp;gt; 0.25, (Fe,Mg) O remains insulating up to the highest studied pressures, implying a Mott-insulator to band-insulator phase transition at the HS-LS transformation.

  • 45.
    Mukhamedov, B. O.
    et al.
    National University of Science and Technology MISIS, Russia.
    Ponomareva, A. V.
    National University of Science and Technology MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Spinodal decomposition in ternary Fe-Cr-Co system2017In: JOURNAL OF ALLOYS AND COMPOUNDS, ISSN 0925-8388, Vol. 695, p. 250-256Article in journal (Refereed)
    Abstract [en]

    Using the exact muffin-tin orbitals method in conjunction with the coherent potential approximation we have studied the tendency towards spinodal decomposition of solid solution in ternary Fe-Cr-Co system. In addition, we have estimated the Curie temperature of the alloys, and considered the influence of the magnetic state on the decomposition thermodynamics of the ternary alloys. Using the mean field approximation, we have estimated the finite temperature effects on the alloys free energy. We predict that an increase Co and Cr content in the ternary Fe-Cr-Co system increases the tendency of the bcc (alpha)-FexCryCoz alloys towards the spinodal decomposition. Because of this, high magnetic properties and high thermal stability of these properties can be expected in the Fe-Cr-Co alloys with high Co content. (C) 2016 Elsevier B.V. All rights reserved.

  • 46.
    Fashandi, Hossein
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Dahlqvist, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Palisaitis, Justinas
    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.
    Abrikosov, Igor
    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.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Andersson, Mike
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, Faculty of Science & Engineering.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Synthesis of Ti3AuC2, Ti3Au2C2 and Ti3IrC2 by noble metal substitution reaction in Ti3SiC2 for high-temperature-stable Ohmic contacts to SiC2017In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 16, no 8, p. 814-818Article in journal (Refereed)
    Abstract [en]

    The large class of layered ceramics encompasses both van der Waals (vdW) and non-vdW solids. While intercalation of noble metals in vdW solids is known, formation of compounds by incorporation of noble-metal layers in non-vdW layered solids is largely unexplored. Here, we show formation of Ti3AuC2 and Ti3Au2C2 phases with up to 31% lattice swelling by a substitutional solid-state reaction of Au into Ti3SiC2 single-crystal thin films with simultaneous out-diffusion of Si. Ti3IrC2 is subsequently produced by a substitution reaction of Ir for Au in Ti3Au2C2. These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 degrees C in air. The present results, by combined analytical electron microscopy and ab initio calculations, open avenues for processing of noble-metal-containing layered ceramics that have not been synthesized from elemental sources, along with tunable properties such as stable electrical contacts for high-temperature power electronics or gas sensors.

  • 47.
    Wang, Fei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Holec, David
    University of Leoben, Austria.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Muecklich, Frank
    University of Saarland, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 127, p. 124-132Article in journal (Refereed)
    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.

  • 48.
    Feng, Qingguo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jönsson, Johan
    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. NUST MISIS, Russia.
    Topological transitions of the Fermi surface of osmium under pressure: an LDA plus DMFT study2017In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, article id 033020Article in journal (Refereed)
    Abstract [en]

    The influence of pressure on the electronic structure of Os has attracted substantial attention recently due to reports on isostructural electronic transitions in this metal. Here, we theoretically investigate the Fermi surface of Os from ambient to high pressure, using density functional theory combined with dynamical mean field theory. Weprovide a detailed discussion of the calculated Fermi surface and its dependence on the level of theory used for the treatment of the electron-electron interactions. Although we confirm that Os can be classified as weakly correlated metal, the inclusion of local quantum fluctuations between 5d electrons beyond the local density approximation explains the most recent experimental reports regarding the occurrence of electronic topological transitions in Os.

  • 49.
    Caffrey, Nuala M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor 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. NUST MISIS, Russia; Tomsk State University, Russia.
    Changes in work function due to NO2 adsorption on monolayer and bilayer epitaxial graphene on SiC(0001)2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 20, article id 205411Article in journal (Refereed)
    Abstract [en]

    The electronic properties of monolayer graphene grown epitaxially on SiC(0001) are known to be highly sensitive to the presence of NO2 molecules. The presence of small areas of bilayer graphene, on the other hand, considerably reduces the overall sensitivity of the surface. We investigate how NO2 molecules interact with monolayer and bilayer graphene, both free-standing and on a SiC(0001) substrate. We show that it is necessary to explicitly include the effect of the substrate in order to reproduce the experimental results. When monolayer graphene is present on SiC, there is a large charge transfer from the interface between the buffer layer and the SiC substrate to the molecule. As a result, the surface work function increases by 0.9 eV after molecular adsorption. A graphene bilayer is more effective at screening this interfacial charge, and so the charge transfer and change in work function after NO2 adsorption is much smaller.

  • 50.
    Wang, Fei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia; Tomsk State University, Russia.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Muecklich, Frank
    University of Saarland, Germany.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 17, p. 174201-Article in journal (Refereed)
    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.

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