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First Principle Studies of Functional Materials: Spintronics, Hydrogen Storage and Cutting Tools
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The properties of functional materials have been studied with density functional theory.

The first type of materials that have been investigated is the so called diluted magnetic semiconductors. It is a new class of materials that could offer enhanced functionality by making use of spin in addition to the charge of the electron. (Mn,Al) co-doped ZnO has been investigated regarding the Al significance on ferromagnetic behavior using density functional theory within the generalized-gradient approximation plus on-site Coulomb interaction. Despite the presence of Al the system always shows antiferromagnetic behavior. The role of intrinsic defects on ferromagnetism in pure and Cr doped In2O3 was also studied. For pristine In2O3, In vacancy and O interstitial states are completely spin polarized. Moreover, these hole states will create Cr ions in mixed valence state, giving rise to a strong ferromagnetic coupling.

The second type of functional materials studied are hydrogen storage materials for mobile applications. These materials are considered as alternative if hydrogen is to replace fossil fuels as a energy carrier. In the view of this a series of compounds containing boron, nitrogen and hydrogen has been examined with respect to electronic structure, dehydrogenation energy and hydrogen diffusion properties. One compound, NH3BH3, has many desirable properties as a hydrogen storage material. In an effort to improve those properties, one of the H atoms in the NH3 group was replaced by Li, Na or Sr. The calculated hydrogen removal energies of the hydrogen release reactions were found to be significantly improved.

Finally, a coating material, Al2O3, for wear resistant coatings on high performance cemented carbide cutting tools has been investigated. Chemical vapor deposition grown Al2O3 has been used for decades by the industry. To improve the growth process H2S is added to the gas mixture. The catalytic effect of H2S on the AlCl3/H2/CO2/HCl chemical vapor deposition process has been investigated on an atomistic scale. By applying a combined approach of thermodynamic modeling and density functional theory it seems that H2S acts as mediator for the oxygenation of the Al-surface which will in turn increase the growth rate of Al2O3.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 60 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 871
Keyword [en]
spintronics, hydrogen storage, coating materials
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-160270ISBN: 978-91-554-8191-9 (print)OAI: oai:DiVA.org:uu-160270DiVA: diva2:449068
Public defence
2011-12-02, Siegbahnsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2011-11-11 Created: 2011-10-19 Last updated: 2011-11-23Bibliographically approved
List of papers
1. Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory
Open this publication in new window or tab >>Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory
2010 (English)In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 150, no 13-14, 663-665 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate by means of first-principles calculations that the high Curie temperature observed in Cr-doped In2O3 is mediated by intrinsic p-type defects, namely In vacancies or O interstitials. Charge transfer from Cr 3d states to the hole states formed by these defects makes Cr ions in the mixed valence state, giving rise to a strong ferromagnetic coupling. Calculated formation energies of various defects also show that doping Cr in In2O3 could greatly lower the formation energies of p-type intrinsic defects even in oxygen-deficient growth conditions. These results advance our understanding of the underlying physics of diluted magnetic oxides. (C) 2009 Elsevier Ltd. All rights reserved.

Keyword
Semiconductors, Impurities in semiconductors, Electronic band structure
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-136997 (URN)10.1016/j.ssc.2009.12.022 (DOI)000276508300029 ()
Available from: 2010-12-14 Created: 2010-12-14 Last updated: 2017-12-11Bibliographically approved
2. Structural and energetic analysis of the hydrogen storage materials LiNH2BH3 and NaNH2BH3 from ab initio calculations
Open this publication in new window or tab >>Structural and energetic analysis of the hydrogen storage materials LiNH2BH3 and NaNH2BH3 from ab initio calculations
Show others...
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 13, 132102- p.Article in journal (Refereed) Published
Abstract [en]

Ammonia borane (NH3BH3) possesses many appealing properties as a hydrogen storage material; however, the release of trace amounts of borazine during the desorption process is troublesome. Recently, it was found that substitution of one of the H atoms in the NH3 group by Li or Na could significantly improve the hydrogen desorption properties. The resulting lithium amidoborane (LiNH2BH3) and sodium amidoborane (NaNH2BH3) compounds have been studied by us using density-functional theory. Specifically, we have succeeded in determining the detailed crystal structures of LiNH2BH3 and NaNH2BH3, including the atomic positions in their respective unit cells. Calculated hydrogen removal energies of the hydrogen release reactions are found to be in good agreement with the experimental trend.

Keyword
ab initio calculations, ammonium compounds, boron compounds, crystal structure, density functional theory, desorption, hydrogen storage, lithium compounds, reaction kinetics theory, surface chemistry
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-129060 (URN)10.1103/PhysRevB.79.132102 (DOI)000265942800002 ()
Available from: 2010-08-06 Created: 2010-08-05 Last updated: 2017-12-12
3. An ab-initio study of (Mn,Al) doped ZnO including strong correlation effects
Open this publication in new window or tab >>An ab-initio study of (Mn,Al) doped ZnO including strong correlation effects
2012 (English)In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 44, no 6, 1095-1097 p.Article in journal (Refereed) Published
Abstract [en]

(Mn,Al)-codoped ZnO has been investigated by means of first-principles calculations using density-functional theory within the generalized-gradient approximation plus on-site Coulomb interaction (GGA + U) to take into the strong correlations on the Mn site. It is found that for several Al-Mn distances, the system shows always an antiferromagnetic behavior. This is explained by the fact that even with the correct electronic structure described with the GGA + U scheme, the extra electron brought by Al is localized in the host conduction band, and therefore does not modify the occupation of the Mn atoms, suggesting that the antiferromagnetic interaction is still dominant. 

Keyword
first-principles, ab-initio, strong correlation, DFT
National Category
Physical Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-160241 (URN)10.1016/j.physe.2010.12.007 (DOI)000305104600041 ()
Conference
European Materials Research Symposium on Science and Technology of Nanotubes, Nanowires and Graphene (EMRS), Strasbourg, FRANCE, JUN 07-11, 2010
Projects
Fredrik Silvearv
Available from: 2011-10-18 Created: 2011-10-18 Last updated: 2017-12-08Bibliographically approved
4. Tuning magnetic properties of In2O3 by control of intrinsic defects
Open this publication in new window or tab >>Tuning magnetic properties of In2O3 by control of intrinsic defects
Show others...
2010 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 89, no 4, 47005- p.Article 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. Copyright (C) EPLA, 2010

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-137617 (URN)10.1209/0295-5075/89/47005 (DOI)000276100300029 ()
Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11Bibliographically approved
5. Understanding the catalytic effects of H2S on CVD-growth of α-alumina: Thermodynamic gas-phase simulations and density functional theory
Open this publication in new window or tab >>Understanding the catalytic effects of H2S on CVD-growth of α-alumina: Thermodynamic gas-phase simulations and density functional theory
Show others...
2011 (English)In: Proceedings of the 38th International Conference on Metallurgical Coatings and Thin Films (ICMCTF) — ICMCTF 2011, 2011, 1771-1779 p.Conference paper, Published paper (Refereed)
Abstract [en]

The catalytic effect of H2S on the AlCl3/H2/CO2/HCl chemical vapor deposition (CVD) process has been investigated on an atomistic scale. We apply a combined approach with thermodynamic modeling and density functional theory and show that H2S acts as mediator for the oxygenation of the Al-surface which will in turn increase the growth rate of Al2O3. Furthermore we suggest surface terminations for the three investigated surfaces. The oxygen surface is found to be hydrogenated, in agreement with a number of previous works. The aluminum surfaces are Cl-terminated in the studied CVD-process. Furthermore, we find that the AlClO molecule is a reactive transition state molecule which interacts strongly with the aluminum and oxygen surfaces.

Series
Surface and Coatings Technology, 206:7
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-160243 (URN)10.1016/j.surfcoat.2011.09.018 (DOI)
Conference
The 38th International Conference on Metallurgical Coatings and Thin Films (ICMCTF), May 2 to 6, 2011, San Diego, CA, USA
Available from: 2011-10-18 Created: 2011-10-18 Last updated: 2013-03-06Bibliographically approved
6.
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7. A theoretical study of possible point defects incorporated into CVD grown α-alumina
Open this publication in new window or tab >>A theoretical study of possible point defects incorporated into CVD grown α-alumina
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-160269 (URN)
Available from: 2011-10-19 Created: 2011-10-19 Last updated: 2011-11-23

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