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High-pressure crystal structure studies of Fe, Ru and Os
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. (Condensed Matter Theory Group)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. (Condensed Matter Theory Group)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. (Condensed Matter Theory Group)
2004 (English)In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 65, no 8-9, 1565-1571 p.Article in journal (Refereed) Published
Abstract [en]

In order to reveal structural trends with increasing pressure in d transition metals, we performed full potential linear muffin-tin orbital calculations for Fe, Ru, and Os in the hexagonal close packed structure. The calculations cover a wide volume range and demonstrate that all these hexagonal close-packed metals have non-ideal c/a at low pressures which, however, increases with pressure and asymptotically approaches the ideal value at very high compressions. These results are in accordance with most recent experiment for Ru and Os. The experimental data for iron is not conclusive, but it is believed that the c/a ratio decreases weakly with increasing pressure at moderate compression. Since, the experimental and calculated equations of state for iron are in increasingly good agreement with increasing pressure, it is possible that either the negative c/a trend is valid only for a restricted pressure range, or related to the experimental difficulties (e.g. non-hydrostaticity).

Place, publisher, year, edition, pages
2004. Vol. 65, no 8-9, 1565-1571 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-91799DOI: 10.1016/j.jpcs.2003.11.043OAI: oai:DiVA.org:uu-91799DiVA: diva2:164648
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Materials Design from ab initio Calculations
Open this publication in new window or tab >>Materials Design from ab initio Calculations
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a theoretical study of bulk materials using ab initio methods based on the density functional theory (DFT).

Crystallographic structural phase transformations and phase stability for 5f-dioxides, ABO3 perovskites, and ABO4 compounds have been extensively studied. Different approaches such as static total energy calculations, elastic stability and dynamical stability (phonon calculations) criteria have been used to determine the phase stability. As a special case, the lattice dynamics of solid Xe has been studied as a function of pressure.

Dielectric functions and optical constants have been calculated for solar energy cell system CuIn1-xGaxSe2 with concentrations x=0, 0.25, 0.5 and 1.0 as well as for C60, PbWO4 and δ-AlOOH. The absorption coefficient provides information about the optimum solar energy conversion efficiency. We have derived absorption coefficients for a number of compounds. Comparisons between the calculated and experimental dielectric functions and absorption coefficients have been made.

The main part of this thesis focuses on the nanolayered ternary compounds M N+1AXN (MAX), where N = 1, 2 or 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N. These ternary carbides and nitrides combine unusual properties of both metals and ceramics. They exhibit high hardness, but fully reversible plasticity, and negligible thermoelectric power. These excellent properties make the MAX phases another new class of materials with versatile technological applications. Our work presents a systematic study of the electronic, bonding, elastic and optical properties of the MAX phases. A new MAX phase-Ti4SiC3, is calculated to be stable, and at the same time also been synthesized by experimentalists. Surface energy calculations have also been performed for the (0001) surface of the Ti-Si-C system. The general relations between the electronic structure and materials properties of the MAX phases have been elaborated in the thesis.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 66 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 982
Keyword
Physics, DFT, MAX, Optics, phase transition, phonon, EOS, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-4274 (URN)91-554-5976-5 (ISBN)
Public defence
2004-05-26, Pohemsalen, Angstrom Laboratory, Uppsala, 10:00
Opponent
Supervisors
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2012-11-20Bibliographically approved

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Ahuja, RajeevJohansson, Börje

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