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Structure Determination of the 4d Metal Diborides: A Quantum Mechanical Study
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. oorganisk kemi.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. oorganisk kemi.
2006 (English)In: The Journal of Physical Chemistry B, Vol. 110, no 11, 5367-5371 p.Article in journal (Refereed) Published
Abstract [en]

Metal diborides (MB2) often have interesting thermal, mechanical, and superconducting properties. MgB2 was put into focus some years ago for its high transition temperature (39 K) in combination with its simple AlB2 structure. The boron structure in MB2 is assumed to be dependent on the electron transfer from the nearby positioned metal atoms. An electronic and structural comparison has been performed here for various initially planar and puckered transition-metal borides, using quantum mechanical density functional theory (DFT) calculations under periodic boundary conditions. In comparison to MgB2, the experimentally planar transition-metal diborides (ZrB2, NbB2, and MoB2) and the experimentally puckered ones (TcB2, RuB2, RhB2, and PdB2) have been examined. The results indicate that the energetic stability generally follows the experimentally obtained results. The metals that are less electronegative than boron donate electrons to boron, which in turn induce planar boron structures (graphitic-like). The metals that prefer to be planar donate more than one electron, while the trend for metals which favor puckered B structures is that they donate less than one electron per metal atom. Two donated electrons per metal atom (or very close to) will result in the most stable AlB2 structure.

Place, publisher, year, edition, pages
2006. Vol. 110, no 11, 5367-5371 p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-80004DOI: doi:10.1021/jp056652xOAI: oai:DiVA.org:uu-80004DiVA: diva2:107918
Available from: 2006-04-20 Created: 2006-04-20 Last updated: 2014-04-29
In thesis
1. The Effect of Boron in Metal Borides and BN – A Theoretical Approach
Open this publication in new window or tab >>The Effect of Boron in Metal Borides and BN – A Theoretical Approach
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Boron, B, has many interesting electronic and structural properties, which makes it an ideal material for technical and industrial needs. The different binary materials that have been in focus in the present thesis, do all include B; metal diborides (MB2), cubic boron nitride (c-BN) forming an interface with diamond, and various phases of BN [cubic (c-BN), hexagonal (h-BN), wurtzitic (w-BN), and rhombohedral (r-BN)]. Density Functional Theory (DFT) methods have been used in studying structural geometries, energetical stabilities, electronic properties, and surface reactivity.

A structural and electronic comparison has been made for various MB2 compounds in planar and puckered structural forms. The resulting MB2 structure was found to correlate to the degree of electron transfer from the metal atom to B. A transfer of more than one electron was observed to induce a planar B structure. This is to be compared with the planar MgB2 structure, for which an electron transfer of two electrons was observed.

The initial nucleation of c-BN onto a diamond substrate has also been focused in the present thesis. This step has experimentally been found to be critical for a phase-pure c-BN thin film growth to occur. The evolution of an interfacial diamond//BN structure was investigated, with the purpose to simulate a layer-by-layer growth of c-BN. The obtained results were found to strongly support the experimental findings, in that there is a need for an extra energy in order to avoid non-cubic phases in the closest vicinity to the substrate. However, the simulations showed that it is possible to diminish this need of extra energy by completely terminating the surface by species like H or F. These calculations also showed that terminated diamond//BN generally show a stronger interfacial bond energy, thereby improving the adhesion to the diamond substrate. The importance with surface termination was not found crucial for thicker BN adlayers.

A combined effect of doping and surface termination was investigated for the various BN allotropes, (using O, C, and Si). The electron induced in c-BN by the O (or C) dopant was observed to move towards the surface B atoms, and thereby creating a more reactive surface. For the upper surface N atoms, doping was observed to create a less reactive N surface. The Si dopants did only show a positive effect on surface reactivity at the B surface sites on both h-BN (001) and r-BN (001) surfaces.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 87 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1124
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-218393 (URN)978-91-554-8879-6 (ISBN)
Public defence
2014-04-01, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-10 Created: 2014-02-11 Last updated: 2014-04-29

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Pallas, AnnaLarsson, Karin

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