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

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 CeH2.52. 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. (C) 2009 Elsevier Masson SAS. All rights reserved.