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Examination of the reliability of X-ray techniques for determining hydrogen-induced volume changes
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 10, 104118- p.Article in journal (Refereed) Published
Abstract [en]

The Bragg peaks in x-ray diffraction experiments are generally taken to be a reliable measure of the average lattice distance in crystals. We show that this assumption can be misleading when determining hydrogen-induced volume changes. Experiments based on simultaneous determination of the position of the Bragg peak and the sample volume of an Fe/V(001) superlattice while expanding the lattice by in situ hydrogen loading serve as an illustration of this counter-intuitive effect.

Place, publisher, year, edition, pages
2008. Vol. 78, no 10, 104118- p.
Keyword [en]
hydrogen, iron, metallic superlattices, vanadium, X-ray diffraction
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-101139DOI: 10.1103/PhysRevB.78.104118ISI: 000259690400035OAI: oai:DiVA.org:uu-101139DiVA: diva2:211972
Available from: 2009-04-20 Created: 2009-04-20 Last updated: 2017-12-13
In thesis
1. Influence of Self-trapping, Clamping and Confinement on Hydrogen Absorption
Open this publication in new window or tab >>Influence of Self-trapping, Clamping and Confinement on Hydrogen Absorption
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dissociation of hydrogen molecules at surfaces is the first step in the absorption process. If the absorbing material is covered by an oxide, this layer will determine the effective uptake rate of an underlying absorbing material. This effect is illustrated when determining the rate of transport of hydrogen through amorphous aluminium oxide layers. The transport rate was determined to be strongly thickness dependent.

Hydrogen absorbed in a transition metal causes a volume expansion generated by a strain field around the absorbed hydrogen. This strain field causes a self-trapping of the hydrogen and a temperature dependent distribution in the atomic distances. The local strain field generated by the self-trapping process is found to be crucial for understanding both the hydrogen induced volume expansion as well as the diffusion of hydrogen. Ab-initio molecular dynamics simulations were used to reveal the temperature dependence of the unbinding of the hydrogen and the local strain field and its influence on the diffusion rate. The symmetry of the local strain field is also important for phase formation in metallic films and superlattices which are clamped to a substrate. As the thicknesses reduced from 50 to 10 nm thick vanadium films, substantial finite size effects become apparent in the phase diagrams. The volume change associated with the strain field cannot be accurately measured using x-ray diffraction because of its sensitivity to local arrangements of atoms. X-ray and neutron reflectivity were found to be more reliable probes of global effects of the sumof the local strainfields.

Finite size effects in extremely thin V layers were also explored in metallic superlattices composed of iron and vanadium. The co-existence region, composed of a hydrogen gas and a solid-like phase, was found to be suppressed by at least 100 K to below 300 K. The hydrogen-hydrogen interaction can also be influenced by the electronic states in the non hydrogen absorbing layers, as demonstrated when comparing hydrogen absorption in Fe/V and Cr/V superlattices.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 798
Keyword
hydrogen diffusion, thin films, superlattices, phase transitions, confinement, clamping, self-trapping, finite-size effect
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-140329 (URN)978-91-554-7983-1 (ISBN)
Public defence
2011-02-18, Häggsalen, Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 728Available from: 2011-01-31 Created: 2011-01-04 Last updated: 2011-03-21Bibliographically approved

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Pálsson, Gunnar K.Rennie, AdrianHjörvarsson, Björgvin

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