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Local structure and lattice defects in metal hydrides and hydrogen absorbing intermetallic compounds

English title Local structure and lattice defects in metal hydrides and hydrogen absorbing intermetallic compounds
Applicant Cerny Radovan
Number 107916
Funding scheme Project funding (Div. I-III)
Research institution Laboratoire de Cristallographie Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Condensed Matter Physics
Start/End 01.09.2005 - 30.09.2008
Approved amount 135'304.00
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Keywords (10)

Powder diffraction; Pair Distribution Function; local order; metal hydride; line profile analysis; local structure; crystallography; hydrogen storage; hydride; crystal structure

Lay Summary (English)

Lead
Lay summary
Many disordered crystalline materials show chemical short range order and relaxation of neighbouring atoms. In these interesting materials long-range order exists but significant structural distortions are also present that are not reflected in the average structure, for example, in the case of the metal hydrides.

Metal and complex hydrides are examples of compounds where the atomic order, long and/or short range, are the mechanisms of controlling their properties like conductivity, optical state, magnetic interaction or hydrogen storage capacity.

Main subject of this project is to clarify the situation about the local order of hydrogen atoms in a crystal structure of a metallic compound absorbing hydrogen and in its hydride. As the metal hydrides are mostly available only as a fine powder, we are using powder diffraction methods.

Studying these challenging materials is notoriously difficult. Recently, significant advances have been made using the atomic Pair Distribution Function (PDF) analysis of powder diffraction data coupled with the use of advanced X-ray and neutron sources and fast computers (http://www.totalscattering.org/). The PDF gives the volume normalized probability of finding an atom at a given distance r from another atom. In other words it can be understood as a bond length distribution of the material weighted by the respective scattering powers of the contributing atoms. The study of the PDF on different length scales allows one to obtain information about the nano-scale structure of materials.

We are currently studying the hydrides of Laves phases YFe2 and YMn2. The hydrogen in this compounds is at room temperature distributed (disordered) over many positions, but at low temperature it creates metal-hydrogen complexes (ordered). From our recent experiments we can already do some preliminary conclusions: The PDFs in ordered and disordered states look very similar up to the radial distance of ~ 8 Å and then they start to differ more significantly. This observation holds for all samples. It gives us the hope that our initial idea that locally (on the nano-scale) the structure stays the same in ordered and disordered state will be confirmed.

The PDF technique has the potential to become nearly a routine type of analysis and a useful tool for structural chemists in the next decades, and will help significantly in our understanding of structures at the atomic level.

The project contains a further development of the program FOX (http://objcryst.sourceforge.net/, developed within the NSF project no. 21-53847.98). The program FOX was recognized as one of the most powerful and mostly used tool for the crystal structure determination from powder diffraction data (http://sdpd.univ-lemans.fr/sdpdrr2/results/).

A good control of the powder diffraction method clearly constitutes a competitive edge, and Swiss laboratories appear to be particularly well positioned in that respect due to their well-known tradition in this domain and because of the easy access to new radiation sources like the Swis-Norwegian Beamline at the ESRF Grenoble, Swiss Light Source and SINQ at the PSI Villigen.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Local deuterium order in apparently disordered Laves phase deuteride YFe2D4.2
Ropka J, Cerny R, Paul-Boncour V (2011), Local deuterium order in apparently disordered Laves phase deuteride YFe2D4.2, in JOURNAL OF SOLID STATE CHEMISTRY, 184(9), 2516-2524.
Deuterium ordering in Laves-phase deuteride YFe2D4.2
Ropka J, Cerny R, Paul-Boncour V, Proffen T (2009), Deuterium ordering in Laves-phase deuteride YFe2D4.2, in JOURNAL OF SOLID STATE CHEMISTRY, 182(7), 1907-1912.

Associated projects

Number Title Start Funding scheme
131811 Bimetallic borohydrides: hydrogen storage and superionic conductivity. 01.10.2010 Project funding (Div. I-III)
122123 Local order in GdFe2 and LaNi5 hydrides and in new series of borohydrides 01.10.2008 Project funding (Div. I-III)

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