Change search
Refine search result
1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Mozafari, Elham
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Shulumba, Nina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia.
    Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture from ab initio molecular dynamics calculations2016In: Physical Review B, ISSN 2469-9950, Vol. 94, no 5, article id 054111Article in journal (Refereed)
    Abstract [en]

    We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local moments picture and ab initio molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance the efficiency of the simulations of elastic properties using the recently introduced method: symmetry imposed force constant temperature-dependent effective potential (SIFC-TDEP). We have chosen cubic paramagnetic CrN as a model system. This is done due to its technological importance and its demonstrated strong coupling between magnetic and lattice degrees of freedom. We have studied the temperature-dependent single-crystal and polycrystalline elastic constants of paramagentic CrN up to 1200 K. The obtained results at T = 300 K agree well with the experimental values of polycrystalline elastic constants as well as the Poisson ratio at room temperature. We observe that the Young’s modulus is strongly dependent on temperature, decreasing by 14% from T = 300 K to 1200 K. In addition we have studied the elastic anisotropy of CrN as a function of temperature and we observe that CrN becomes substantially more isotropic as the temperature increases. We demonstrate that the use of Birch law may lead to substantial errors for calculations of temperature induced changes of elastic moduli. The proposed methodology can be used for accurate predictions of mechanical properties of magnetic materials at temperatures above their magnetic order-disorder phase transition.

  • 2.
    Raza, Zamaan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Shulumba, Nina
    Linköping University, Department of Physics, Chemistry and Biology. University of Saarland, Germany.
    Nuala, Mai Caffrey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Dubrovinsky, Leonid
    University of Bayreuth, 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.
    First-principles calculations of properties of orthorhombic iron carbide Fe7C3 at the Earths core conditions2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 21, article id 214112Article in journal (Refereed)
    Abstract [en]

    A recently discovered phase of orthorhombic iron carbide o-Fe7C3 [Prescher et al., Nat. Geosci. 8, 220 (2015)] is assessed as a potentially important phase for interpretation of the properties of the Earths core. In this paper, we carry out first-principles calculations on o-Fe7C3, finding properties to be in broad agreement with recent experiments, including a high Poissons ratio (0.38). Our enthalpy calculations suggest that o-Fe7C3 is more stable than Eckstrom-Adcock hexagonal iron carbide (h-Fe7C3) below approximately 100 GPa. However, at 150 GPa, the two phases are essentially degenerate in terms of Gibbs free energy, and further increasing the pressure towards Earths core conditions stabilizes h-Fe7C3 with respect to the orthorhombic phase. Increasing the temperature tends to stabilize the hexagonal phase at 360 GPa, but this trend may change beyond the limit of the quasiharmonic approximation.

  • 3.
    Shulumba, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Vibrations in solids: From first principles lattice dynamics to high temperature phase stability2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis I introduce a new method for calculating the temperature dependent vibrational contribution to the free energy of a substitutionally disordered alloy that accounts for anharmonicity at high temperatures. This method exploits the underlying crystal symmetries in an alloy to make the calculations tractable. The validity of this approach is demonstrated by constructing the phase diagram via direct minimization of the Gibbs free energy of a notoriously awkward and technologically important system, Ti1-xAlxN. The vibrational entropy including anharmonic effects is shown to be large and comparable to the configurational entropy at high temperatures, and with its inclusion, the theoretical miscibility gap of Ti1-xAlxN is reduced from 6560 K to 2860 K, in line with atom probe experiments. A similar treatment of Zr1-xAlxN and Hf1-xAlxN alloys suggests that mass disorder has a minimal effect on phase stability compared with chemical ordering. My method is also capable of demonstrating that Hf1-xAlxN, which is dynamically unstable at room temperature, is stabilised at high temperatures. Moreover I develop a new method of computing temperature dependent elastic constants for alloys from their phonon spectra, and show that for Ti1-xAlxN, the elastic anisotropy is found to increase with temperature, helping to explain the spinodal decomposition.

    The effects of lattice dynamics on phase stability, mechanical, magnetic and transport properties on other materials are also examined. Four specific systems are discussed in detail. Firstly, in the case of CrN, lattice vibrations are shown to decrease the antiferromagnetic to paramagnetic phase transition temperature from 500 K to 380 K, in line with experimental evidence. Secondly, a temperature/pressure induced phase transition in AlN becomes much more facile than in the quasiharmonic approximation, and the thermal conductivity of the rocksalt phase is shown to be much lower than that of the wurtzite phase, as a result of the increased anharmonicity in the rocksalt structure. Thirdly, the temperature dependence of elastic constants of TiN becomes more isotropic as the temperature increases. Finally, iron carbides are evaluated as potentially important phases at the Earth’s core; specifically, calculating the Gibbs free energy of a recently discovered orthorhombic phase of Fe7C3 demonstrates that it is not stable relative to the known hexagonal phase at extreme pressure and temperatures.

  • 4.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Mozafari, Elham
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Steneteg, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab initio molecular dynamics2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 17, p. 174108-Article in journal (Refereed)
    Abstract [en]

    We present a theoretical first-principles method to calculate the free energy of a magnetic system in its high-temperature paramagnetic phase, including vibrational, electronic, and magnetic contributions. The method for calculating free energies is based on ab initio molecular dynamics and combines a treatment of disordered magnetism using disordered local moments molecular dynamics with the temperature-dependent effective potential method to obtain the vibrational contribution to the free energy. We illustrate the applicability of the method by obtaining the anharmonic free energy for the paramagnetic cubic and the antiferromagnetic orthorhombic phases of chromium nitride. The influence of lattice dynamics on the transition between the two phases is demonstrated by constructing the temperature-pressure phase diagram.

  • 5.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA.
    Raza, Zamaan
    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. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia / LACOMAS Laboratory, Tomsk State University, Tomsk, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Influence of vibrational free energy on the phase stability of alloys from first principles2015Manuscript (preprint) (Other academic)
    Abstract [en]

    We have developed a method to accurately and efficiently determine the vibrational free energy as a function of temperature and pressure for substitutional alloys from first principles. Taking the example of the technologically important hard coating alloy Ti1-xAlxN as an example, we investigate the effect on the vibrational free energy of substituting Ti for other group IV elements. By constructing the phase diagrams for these three alloys, we show why Zr1-xAlxN and Hf1-xAlxN are so difficult to experimentally synthesise in a metastable solid solution: both have solubility regions that span only a small low-AlN concentration range at temperatures above 1500 K. Moreover, Hf1-xAlxN is dynamically unstable at low temperatures and across most of the concentration range. We also show the chemical and thermal expansion effects dominate mass disorder in the Gibbs free energy of mixing.

  • 6.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA.
    Raza, Zamaan
    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, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany.
    Barrirero, Jennifer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Functional Materials, Saarland University, Campus D3 3, Saarbrücken, Germany.
    Mücklich, Frank
    Functional Materials, Saarland University, Campus D3 3, Saarbrücken, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia / LACOMAS Laboratory, Tomsk State University, Tomsk, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Anharmonicity changes the solid solubility of an alloy at high temperatures2015Manuscript (preprint) (Other academic)
    Abstract [en]

    We have developed a method to accurately and efficiently determine the vibrational free energy as a function of temperature and volume for substitutional alloys from first principles. Taking Ti1−xAlxN alloy as a model system, we calculate the isostructural phase diagram by finding the global minimum of the free energy, corresponding to the true equilibrium state of the system. We demonstrate that the anharmonic contribution and temperature dependence of the mixing enthalpy have a decisive impact on the calculated phase diagram of a Ti1−xAlxN alloy, lowering the maximum temperature for the miscibility gap from 6560 K to 2860 K. Our local chemical composition measurements on thermally aged Ti0.5Al0.5N alloys agree with the calculated phase diagram.

  • 7.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA.
    Rogström, Lina
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Raza, Zamaan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnádi, 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. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia / LACOMAS Laboratory, Tomsk State University, Tomsk, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Temperature-dependent elastic properties of Ti1−xAlxN alloys2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 23Article in journal (Refereed)
    Abstract [en]

    Ti1−xAlxN is a technologically important alloy that undergoes a process of high temperature age-hardening that is strongly influenced by its elastic properties. We have performed first principles calculations of the elastic constants and anisotropy using the newly developed symmetry imposed force constant temperature dependent effective potential method, that include lattice vibrations and therefore the effects of temperature, including thermal expansion and intrinsic anharmonicity. These are compared with in situ high temperature x-ray diffraction measurements of the lattice parameter. We show that anharmonic effects are crucial to the recovery of finite temperature elasticity. The effects of thermal expansion and intrinsic anharmonicity on the elastic constants are of the same order, and cannot be considered separately. Furthermore, the effect of thermal expansion on elastic constants is such that the volume change induced by zero point motion has a significant effect. For TiAlN, the elastic constants soften non-uniformly with temperature: C11 decreases substantially when the temperature increases for all compositions, resulting in an increased anisotropy. These findings suggest that an increased Al content and annealing at higher temperatures will result in a harder alloy.

  • 8.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Raza, Zamaan
    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. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA.
    Janzén, Erik
    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. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia; LACOMAS Laboratory, Tomsk State University, Tomsk, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 10, article id 104305Article in journal (Refereed)
    Abstract [en]

    Wurtzite aluminium nitride is a technologically important wide band gap semiconductor with an unusually high thermal conductivity, used in optical applications and as a heatsink substrate. Many of its properties depend on an accurate description of its lattice dynamics, which have thus far only been captured in the quasiharmonic approximation. In this work, we demonstrate that anharmonicity has a considerable impact on its phase stability and transport properties, since anharmonicity is much stronger in the rocksalt phase. We compute a pressure-temperature phase diagram of AlN, demonstrating that the rocksalt phase is stabilised by increasing temperature, with respect to the wurtzite phase. We demonstrate that including anharmonicity, we can recover the thermal conductivity of the wurtzite phase (320 Wm−1K−1 under ambient conditions), and compute the hitherto unknown thermal conductivity of the rocksalt phase (96 Wm−1K−1). We also show that the electronic band gap decreases with temperature. These findings provide further evidence that anharmonic effects cannot be ignored in high temperature applications.

  • 9.
    Steneteg, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Vekilova, Olga
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Shulumba, Nina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Temperature dependence of TiN elastic constants from ab initio molecular dynamics simulations2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 9Article in journal (Refereed)
    Abstract [en]

    Elastic properties of cubic TiN are studied theoretically in a wide temperature interval. First-principles simulations are based on ab initio molecular dynamics (AIMD). Computational efficiency of the method is greatly enhanced by a careful preparation of the initial state of the simulation cell that minimizes or completely removes a need for equilibration and therefore allows for parallel AIMD calculations. Elastic constants C11, C12, and C44 are calculated. A strong dependence on the temperature is predicted, with C11 decreasing by more than 29% at 1800 K as compared to its value obtained at T=0 K. Furthermore, we analyze the effect of temperature on the elastic properties of polycrystalline TiN in terms of the bulk and shear moduli, the Young's modulus and Poisson ratio. We construct sound velocity anisotropy maps, investigate the temperature dependence of elastic anisotropy of TiN, and observe that the material becomes substantially more isotropic at high temperatures. Our results unambiguously demonstrate the importance of taking into account finite temperature effects in theoretical calculations of elastic properties of materials intended for high-temperature applications.

1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf