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Energetics and magnetic properties of V-doped MgO bulk and (001) surface: A GGA, GGA+U, and hybrid density functional study
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 13, 134406- p.Article in journal (Refereed) Published
Abstract [en]

In this work, a first-principles study of the energetic and magnetic properties of V-doped MgO is presented, where both the bulk and (001) surface were investigated. It is found that V assumes a high-spin state with a local moment of about 3 mu(B). In the bulk, the interaction between these local moments is very short ranged and the antiferromagnetic (AFM) ordering is energetically more favorable. The formation of V-V-Mg-V defect clusters is found to weaken the antiferromagnetic coupling in bulk MgO, degenerating the AFM and ferro-magnetic state. However, these clusters are high in energy and will not form at equilibrium conditions. By employing the GGA+U approach, with U=5 eV, the V 3d states on the (001) surface are shifted below the Fermi level, and a reasonable surface geometry was achieved. A calculation with the hybrid HSE03 functional, contradicts the GGA+U results, indicating that the V-MgO surface should be metallic at this concentration. From the energetics it is concluded that, at the modeled concentration, VxOy phases will limit the solubility of V in MgO at equilibrium conditions, which is in agreement with previous experimental findings. In order to achieve higher concentrations of V, an off-equilibrium synthesis method is needed. Finally, we find that the formation energy of V at the surface is considerably higher than in the bulk and V is thus expected to diffuse from the surface into the bulk of MgO.

Place, publisher, year, edition, pages
2010. Vol. 82, no 13, 134406- p.
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-29335DOI: 10.1103/PhysRevB.82.134406ISI: 000282506700012Scopus ID: 2-s2.0-78049370436OAI: oai:DiVA.org:kth-29335DiVA: diva2:393805
Note
QC 20110201Available from: 2011-02-01 Created: 2011-01-31 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Atomistic modelling of functional solid oxides for industrial applications: Density Functional Theory, hybrid functional and GW-based studies
Open this publication in new window or tab >>Atomistic modelling of functional solid oxides for industrial applications: Density Functional Theory, hybrid functional and GW-based studies
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis a set of functional solid oxides for industrial applications have been addressed by first principles and thermodynamical modelling. More specificially, measurable quantities such as Gibbs free energy, geometry and electronic structure have been calculated and compared when possible with experimental data. These are crystalline and amorphous aluminum oxide (Al2O3), Zirconia (ZrO2), magnesium oxide (MgO), indiumoxide (In2O3) and Kaolinite clay (Al2Si2O5(OH)4).

The reader is provided a computation tool box, which contains a set of methods to calculate properties of oxides that are measurable in an experiment. There are three goals which we would like to reach when trying to calculate experimental quantities. The first is verification. Without verification of the theory we are utilizing, we cannot reach the second goal -prediction. Ultimately, this may be (and to some extent already is) the future of first principles methods, since their basis lies within the fundamental quantum mechanics and since they require no experimental input apart from what is known from the periodic table. Examples of the techniques which may provide verification are X-Ray Diffraction (XRD), X-ray Absorption and Emission Spectroscopy (XAS and XES), Electron Energy Loss Spectroscopy and Photo-Emission Spectroscopy (PES). These techniques involve a number of complex phenomena which puts high demands on the chosen computational method/s. Together, theory and experiment may enhance the understanding of materials properties compared to the standalone methods. This is the final goal which we are trying to reach -understanding. When used correctly, first principles theory may play the role of a highly resolved analysis method, which provides details of structural and electronic properties on an atomiclevel. One example is the use of first principles to resolve spectra of multicomponentsamples. Another is the analysis of low concentrations of defects. Thorough analysis of the nanoscale properties of products might not be possible in industry due to time and cost limitations. This leads to limited control of for example low concentrations of defects, which may still impact the final performance of the product. On example within cutting tool industry is the impact of defect contents on the melting point and stability of protective coatings. Such defects could be hardening elements such as Si, Mn, S, Ca which diffuse from a steel workpiece into the protective coating during high temperature machining. Other problems are the solving of Fe from the workpiece into the coating and reactions between iron oxide, formed as the workpiece surface is oxidized, and the protective coating.

The second part of the computational toolbox which is provided to the reader is the simulation of solid oxide synthesis. Here, a formation energy formalism, most often applied to materials intended in electronics devices is applied. The simulation of Chemical Vapour Deposition (CVD) and Physical Vapor Deposition (PVD) requires good knowledge of the experimental conditions, which can then be applied in the theoretical simulations. Effects of temperature, chemical and electron potential, modelled concentration and choice of theoretical method on the heat of formation of different solid oxides with and without dopants are addressed in this work. A considerable part of this Thesis is based upon first principles calculations, more specifically, Density Functional Theory (DFT) After Kohn and Pople received the Nobel Prize in chemistry in 1998, the use of DFT for computational modelling has increased strikingly (see Fig. 1). The use of other first principles methods such as hybrid functionals and the GW approach (see abbreviations for short explanations and chapter 4.5 and 5.3.) have also become increasingly popular, due to the improved computational resources. These methods are also employed in this Thesis.

Place, publisher, year, edition, pages
Stockholm: KTH, 2011
Keyword
density functional theory, oxides, GW
National Category
Condensed Matter Physics Condensed Matter Physics Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-29257 (URN)978-91-7415-868-7 (ISBN)
Public defence
2011-02-18, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
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Supervisors
Note
QC 20110201Available from: 2011-02-01 Created: 2011-01-28 Last updated: 2012-03-28Bibliographically approved

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