Les phases de Laves RNi ( R = La, Ce) existent avec on &art d la stoechiometrie (5 % pour CeNi2 et 10 % $our LaNi2 ) qui se traduit par un desordre structural observe par EXAFS aatour des atomes de nickel. Ces composes absorbent faci lement 1 hydrogene (4.2 H/mole d 25 C) et deviennent amorphes aux RX pour une concentration superieure d 3.5 H/mole. L1etude EXAFS des hydrures au seail K da nickel met en evidence I1augmentation du desordre local autoar des atomes de nickel. De plus,

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... dlhydrog$ne dans le compose CeNi2 entraine un changement de valence du cerium, observe par 18&tade des seuils L111 du c6rium. ABSTRACT -Laves phases compounds (R = La, Ce) exist with a stoechiometry de:%ion (5 % for CeM2 and 10 % for LaNi2 ) which leads to a structural disorder clearly observed by EXAFS at the Ni K-edge. These compounds easily absorb hydrogen up to 4.2 H/mole at room temperature. X-ray diffraction indicates that they are amorphous for hydrogen contents greater than 3.5 H/mole. EXAFS study at the Ni-K edge gives evidence of the increase of the local disorder upon hydrogenation. In addition a change of cerium valency induced by hydrogen absorption in CeNi2 was observed by a Ce LIII edge study.