Title: Coupling XRD, EXAFS and 13C NMR to study the effect of the carbon stoichiometry on the local structure of UC1±x
Authors: CARVAJAL NUNEZ URSULAMARTEL LAURAPRIEUR DAMIENELOIRDI RachelFARNAN IanVITOVA TonyaSOMERS JosephLOPEZ HONORATO Eddie
Citation: INORGANIC CHEMISTRY vol. 52 no. 19 p. 11669-11676
Publisher: AMER CHEMICAL SOC
Publication Year: 2013
JRC N°: JRC77217
ISSN: 0020-1669
URI: pubs.acs.org/IC
http://publications.jrc.ec.europa.eu/repository/handle/JRC77217
DOI: 10.1021/ic402144g
Type: Articles in periodicals and books
Abstract: A series of uranium carbide samples, prepared by arc melting with a C/U ratio ranging from 0.96 to 1.04, has been studied by X-Ray Diffraction (XRD), 13C Nuclear Magnetic Resonance (NMR) and by Extended X-ray Absorption Fine Structure (EXAFS). XRD determines phase uniqueness and the increase of the lattice parameter versus the carbon content. In contrast, 13C NMR detects the different carbon environments in the lattice and in this study, clearly identifies the presence of discrete peaks for carbon in the octahedral lattice site in UC and an additional peak associated with excess carbon in hyperstoichiometric samples. Two peaks associated with different levels of carbon deficiency are detected for all hypostochiometric compositions. In fact, more than one carbon environment is always detected by 13C NMR. This emphasizes the difficulty in obtaining a perfect stoichiometric uranium monocarbide UC1.00. The 13C MAS spectra of uranium carbides exhibit the effects of the carbon content both in the broadening of the peaks and in the Knight shift. An abrupt spectral change occurs between hypo- and hyperstoichiometric samples. The results obtained by EXAFS highlight subtle differences between the different stoichiometries and in the hyperstoichiometric samples. The EXAFS result is consistent with the excess carbon atoms being in the tetrahedral interstitial position and not as dumbbells at the octahedral sites.
JRC Directorate:Nuclear Safety and Security

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