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Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft x-ray emission spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2005 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 72, no 24, 245101- p.Article in journal (Refereed) Published
Abstract [en]

The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2, and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L, C K, Al L, Si L, and Ge M emission spectra are compared with ab initio density-functional theory including core-to-valence dipole matrix elements. A qualitative agreement between experiment and theory is obtained. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L emission of Ti3AlC2. As Al is replaced with Si or Ge, the shoulder disappears. For the buried Al and Si layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and Ti3SiC2, respectively. As a result of relaxation of the crystal structure and the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened. The differences between the electronic structures are discussed in relation to the bonding in the nanolaminates and the corresponding change of materials properties.

Place, publisher, year, edition, pages
2005. Vol. 72, no 24, 245101- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-91300DOI: 10.1103/PhysRevB.72.245101OAI: oai:DiVA.org:uu-91300DiVA: diva2:163985
Available from: 2004-01-29 Created: 2004-01-29 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Carbide and MAX-Phase Engineering by Thin Film Synthesis
Open this publication in new window or tab >>Carbide and MAX-Phase Engineering by Thin Film Synthesis
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Karbid och MAX-fas design med tunnfilmssyntes
Abstract [en]

This thesis reports on the development of low-temperature processes for transition metal carbide and MAX-phase thin film growth. Magnetron sputtering and evaporation, far from thermodynamical equilibrium, have been utilised to engineer the properties of the films by physical and chemical control. Deposition of W, W2C and β-WC1-x films with controlled microstructure, from nanocrystalline to epitaxial, is shown in the W-C system down to 100 oC. W films with upto 20 at% C exhibited an extreme solid-solution hardening effect, with a nanoindentation hardness maximum of 35 GPa. Furthermore, the design of epitaxial ternary carbide films is demonstrated in the Ti1-xVxCy system in the form of controlled unit-cell parameters, strain-free films with a perfect match to the substrate, and ternary epitaxial gradient films. Moreover, phase stabilisation and pseudomorphic growth can be tuned in (Nb,Mo)C and (Ti,W)C films. The results obtained can be used for example to optimise electrical contacts in SiC high-power semiconductor devices.

A large part of this thesis focuses on the deposition of MAX-phases. These compounds constitute a family of thermally stable nanolaminates with composition Mn+1AXn, n=1, 2 or 3, where M is an early transition metal, A is generally a group 13-14 element, and X is C or N. They show a combination of typical ceramic and metallic properties and are also machinable by virtue of the unique deformation behaviour observed only in laminates. So far, the MAX-phases have almost exclusively been prepared by high-temperature sintering and studied in bulk form. However, this thesis establishes a patented seed layer approach for successful MAX-phase thin film depositions down to 750 oC. For the first time, single-phase and epitaxial films of Ti3SiC2, Ti3AlC2 and Ti2AlC have been grown. The method has also been used to synthesise a new MAX-phase, Ti4SiC3. In addition, two previously unreported intergrown MAX-type structures are presented, Ti5Si2C3 and Ti7Si2C5. Combined theoretical and experimental results show the possibility to deposit films with very low bulk resistivity and designed mechanical properties. Furthermore, the demonstration of MAX-phase and carbide multilayer films paves the way for macrostructure engineering, for example, in coatings for low-friction or wear applications.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 70 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 930
Keyword
Inorganic chemistry, Thin films, microstructure, epitaxy, carbide, WC, MAX-phase, Ti3SiC2, DC magnetron sputtering, PVD, Reciprocal Space Mapping, RSM, Oorganisk kemi
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-3972 (URN)91-554-5858-0 (ISBN)
Public defence
2004-02-27, Polhemsalen, Ångström Laboratory, Uppsala, 13:15
Opponent
Supervisors
Available from: 2004-01-29 Created: 2004-01-29 Last updated: 2014-01-24Bibliographically approved
2. 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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