Crystallographic and hydriding properties of the system La1−xCexY2Ni9 (xCe=0, 0.5 and 1) |
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Authors: | M Latroche R Baddour-Hadjean |
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Affiliation: | a Laboratoire de Chimie Métallurgique des Terres Rares LCMTR, Institut des Sciences Chimiques Seine-Amont, CNRS, 2-8 rue Henri Dunant, F-94320 Thiais Cedex, Franceb Laboratoire de Dynamique, Interactions et Réactivité LADIR, Institut des Sciences Chimiques Seine-Amont, CNRS, 2-8 rue Henri Dunant, F-94320 Thiais Cedex, France |
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Abstract: | The structural properties of the system La1−xCexY2Ni9 with xCe=0, 0.5 and 1 have been investigated by electron probe microanalysis, powder X-ray diffraction and absorption spectroscopy. The compound LaY2Ni9 adopts a rhombohedral structure of PuNi3-type (R-3m space group, Z=3). It can be described as an intergrowth between RM5 (Haücke phase) and RM2 (Laves phase) type structures. Among the two available crystallographic sites for R atoms, lanthanum occupies preferentially the site 3a leading to a partially ordered ternary compound. Substitution by cerium involves anisotropic variations of the cell parameter with a decrease of a and an increase of c leading to an overall cell volume reduction. Increasing cerium content does not induce any symmetry change but leads to a statistical distribution of the rare earths over the two sites 3a and 6c involving an evolution toward a pseudo-binary compound. This behavior is related to the intermediate valence state of cerium observed by X-ray absorption spectroscopy. The hydriding properties of the two compounds LaY2Ni9 and CeY2Ni9 are described in relation with their crystallographic structure. |
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Keywords: | RM5 Hydrides X-ray diffraction X-ray absorption spectroscopy Ordering |
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