Fluorescence XAFS study of NaAlH(4) doped with a Ce-based precursor.
NaAlH(4) doped with CeCl(3) was prepared by ball milling and cycled under hydrogen. As-prepared samples and cycled material were investigated by X-ray absorption spectroscopy in order to elucidate the local structure around Ce atoms in the material. It was found that, in contrast to Ti doped NaAlH(4), the oxidation state of the Ce(iii) remains constant during preparation and cycling. Moreover, there is no formation of a bimetallic entity consisting of Ce and Al which is the case in Ti doped samples. Rather, the first shell around Ce consists of a strongly distorted Cl coordination polyhedron with a coordination number considerably below that of CeCl(3). Al atoms are visible as second next neighbors, which indicates that the ball-milled sample is an intimate mixture between CeCl(x) entities and the alanate host matrix. A steady state seems to have been reached after 8 absorption cycles, and no significant changes of the local Ce coordination environment occur after the 9th desorption.
Léon
Aline
A
Institut für Nanotechnologie, Forschungszentrum Karlsruhe GmbH, P.O. Box 3640, 76021 Karlsruhe, Germany. aline.leon@int.fzk.de
Rothe
Jörg
J
Chłopek
Krzysztof
K
Zabara
Oleg
O
Fichtner
Maximilian
M