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Optical gap and native point defects in kaolinite studied by the GGA-PBE, HSE functional, and GW approaches
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.
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 7, 075120- p.Article in journal (Refereed) Published
Abstract [en]

The electronic structure of kaolinite with and without intrinsic defects has been studied by the Perdew-Burke-Ernzerhof (PBE) and Heyd-Scuseria-Ernzerhof (HSE) functionals and by the G0W0 approach. The band gap of defect-free kaolinite was estimated to between 6.2 and 8.2 eV. Analysis of the formation energy of native point defects in kaolinite was carried out under different growth conditions. When the PBE defect formation energy as a function of temperature is considered, the hydroxyl vacancy is compensated by a hydrogen vacancy at a formation energy of 0.45 eV at oxygen-rich and hydrogen-poor conditions. The hydroxyl vacancy acts as a donor whereas the hydrogenvacancy acts as an acceptor, both inducing states in the band gap. The HSE03 hybrid functional increases the defect formation energy and tends to localize and move these states away from the band edges, as compared to the other two methods. Our results imply that intrinsic defects will tune the band gap of kaolinite and influence properties related to its band structure such as the cation retention capability and drug release.

Place, publisher, year, edition, pages
2011. Vol. 84, no 7, 075120- p.
Keyword [en]
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-29296DOI: 10.1103/PhysRevB.84.075120ISI: 000293618900007ScopusID: 2-s2.0-80052420832OAI: diva2:393582
Swedish Research Council
Available from: 2011-01-31 Created: 2011-01-31 Last updated: 2011-09-07Bibliographically 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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