X-ray/neutron diffraction studies and ab initio electronic structure of CeMgNi₄ and its hydride

Jean-Gabriel Roquefere (1) , Samir F. Matar (1) , Jacques Huot (2) , Jean-Louis Bobet (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 Physics Department, Institut de Recherche sur l'Hydroge?ne

The crystal structure of CeMgNi₄ intermetallic compound has been studied by both X-ray and neutron diffraction. Rietveld refinement shows that both 4a and 4c sites are occupied by Ce and Mg. The exchange has been evaluated to be about 15%. The hydrogenation of the sample leads to a decomposition and to the formation of CeH_2.52. Ab initio calculations using pseudo-potential and all-electron DFT methods are performed to explain such an unexpected behaviour. They predict a larger stability of the hydride system in the orthorhombic structure rather than in the cubic one. Anti-bonding Ce–H interactions within the hydride are proposed to assess the observed easy decomposition. Moreover, the metastability introduced by mechanosynthesis (i.e. exchange between Ce and Mg) was also evaluated.

Mots clés: CeMgNi₄; Exchange ratio; Hydrogen storage; Ball-milling; DFT; VASP; ASW

Domaines: Matériaux

Jean-Gabriel Roquefere, Samir F. Matar, Jacques Huot, Jean-Louis Bobet. X-ray/neutron diffraction studies and ab initio electronic structure of CeMgNi₄ and its hydride. Solid State Sciences, 2009, 11 (11), pp.1971-1978. ⟨10.1016/j.solidstatesciences.2009.07.003⟩. ⟨hal-00438180⟩