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Tuning magnetic properties of In2O3 by control of intrinsic defects
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.
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2010 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 89, no 4Article in journal (Refereed) Published
Abstract [en]

The electronic structure and magnetic properties of In2O3 with four kinds of intrinsic point defects (O vacancy, In interstitial, O interstitial, and In vacancy) have been theoretically studied using the density functional theory. The defect energy states of the O vacancy and In interstitial are close to the bottom of conduction band and act as shallow donors, while the defect energy states of the In vacancy and O interstitial are just above the top of the valence band and act as shallow acceptors. Without addition of any magnetic ions, all the hole states are completely spin polarized, while the electron states display no spin polarization. This implies that semiconducting In2O3 can display magnetic ordering, purely due to the intrinsic defects. However, the formation energies for neutral p-type defects are too high to be thermodynamically stable at reasonable temperatures. Nevertheless, it is shown that negative charging can greatly decrease the formation energies of p-type defects, simultaneously removing the local magnetic moments. We conlcude that V-In''' and O-I '' will be the dominant compensating defects as In2O3 is doped with TM ions, such as Sn, Mo, V and Cr. This result is consistent with the general view that the p-type defect is a key feature to mediate ferromagnetic coupling between transition metal ions of dilute concentration in metal oxides.

Place, publisher, year, edition, pages
2010. Vol. 89, no 4
Keyword [en]
ab-initio, doped in2o3, semiconductors, energy, oxide
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-19353DOI: 10.1209/0295-5075/89/47005ISI: 000276100300029ScopusID: 2-s2.0-79051471574OAI: diva2:337400
Swedish Research Council
QC 20110119Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-02-01Bibliographically 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
density functional theory, oxides, GW
National Category
Condensed Matter Physics Condensed Matter Physics Condensed Matter Physics
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)
QC 20110201Available from: 2011-02-01 Created: 2011-01-28 Last updated: 2012-03-28Bibliographically approved

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