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Anomalous temperature dependence of elastic constant c44 in V, Nb, Ta, Pd, and Pt
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2010 (English)In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, 1065-1068 p.Article in journal (Refereed) Published
Abstract [en]

The electrochemical reduction processes on stainless-steel substrates from an aqueous electrolyte composed of nitric acid, Bi3+, HTeO2+, SbO+ and H2SeO3 systems were investigated using cyclic voltammetry. The thin films with a stoichiometry of Bi2Te3, Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 have been prepared by electrochemical deposition at selected potentials. The structure, composition, and morphology of the films were studied by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and electron microprobe analysis (EMPA). The results showed that the films were single phase with the rhombohedral Bi2Te3 structure. The morphology and growth orientation of the films were dependent on the deposition potentials.

Place, publisher, year, edition, pages
2010. Vol. 71, no 8, 1065-1068 p.
Keyword [en]
Chalcogenides; Crystal growth; Electron microscopy; Microstructure
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:uu:diva-95715DOI: 10.1016/j.jpcs.2010.03.007ISI: 000280977000008OAI: oai:DiVA.org:uu-95715DiVA: diva2:170033
Available from: 2007-04-04 Created: 2007-04-04 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Computational Material Design: Diluted Magnetic Semiconductors for Spintronics
Open this publication in new window or tab >>Computational Material Design: Diluted Magnetic Semiconductors for Spintronics
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis deals with the application of ab-initio electronic structure calculations based on density functional theory for material design.

The correlation between magnetic properties and electronic structures has been investigated in detail for diluted magnetic semiconductors (DMS), which have promising application for spintronics devices. The point defects, acting as electron donor or electron acceptor, have been studied for their key role in mediating the long ranged ferromagnetic interaction between transition metal (TM) ions. The electron holes induced by electron acceptor are completely spin polarized in semiconductor and exhibit a very significant efficiency to the ferromagnetic coupling between TM ions. While the electron donor shows a negative effect to the ferromagnetism in the system. The common trend of magnetic interaction and electron charge transfer between TM ions and electron acceptors or electron donators have been outlined. The Coulomb correlation U of d electrons, which could change the energy levels of TM d band respective to the host semiconductor band, also shows a significant influence on the magnetic behavior in DMS.

The crystallography phase transition under high pressure has also been studied for the iron doped with light element, carbon. Our calculated results show that interstitial carbon defect has little effect on the iron's bcc to hcp phase transition under high pressure. The other carbon iron phases, like Fe3C, has also been studied in a wide pressure range.

We also present a first-principles description on the temperature dependence of elastic constant for solids. The total temperature effects are approximated as a sum of two separated parts, the thermal expansion contribution, which gives the normal linearly decreasing effect on the elastic constant with increasing temperature, and the electronic band contribution, which could lead anomalous behavior for thermal elastic constants.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 290
Keyword
Physics, Density functional theory, Diluted magnetic semiconductor, Ferromagnetism, Defect, Phase transition, High pressure, Thermal elastic constant, Fysik
Identifiers
urn:nbn:se:uu:diva-7800 (URN)978-91-554-6855-2 (ISBN)
Public defence
2007-04-26, Polhemsalen, Angstrom Laboratory, Box 530, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-04-04 Created: 2007-04-04Bibliographically approved
2. Structural, Electronic and Mechanical Properties of Advanced Functional Materials
Open this publication in new window or tab >>Structural, Electronic and Mechanical Properties of Advanced Functional Materials
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage.

Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials.

Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies.

MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method.

Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature.

In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 98 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1062
Keyword
DFT, Hydrogen storage, Rechargeable batteries, Amorphization, Electronic structure, Crystal strcuture, Molecular dynamics, Diffusion, Intercalation voltage, High pressure, MAX phases, Mechanical properties, Optical properties, Phase change memory, Spintronics, Magnetism, Correlation effects, Band structure
National Category
Physical Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-205243 (URN)978-91-554-8723-2 (ISBN)
Public defence
2013-09-27, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-09-06 Created: 2013-08-15 Last updated: 2014-01-08Bibliographically approved

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Vitos, LeventeJohansson, BörjeAhuja, Rajeev

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