Ab initio study of the hydrogenation properties of Mg-based binary and ternary compounds Mg2X (X = Ni, Si) and YMgNi4

In this paper the results of ab initio electronic structure investigations of several Mg-based compounds are presented. From our total energy calculations and from the analysis of the electronic factors that control the stability of the intermetallic compounds and their hydrides, we show why Mg2NiH4 is stable while Mg2Si does not absorb hydrogen. Our results are in agreement with recent experimental data on the hydrogenation of Mg2X phases (X = Ni Si, Ge, Sn) of Janot et al., as well as with studies of the role of Si in the destabilization of MgH2 through the formation of M2Si, by Vajo et al. We have also analvzed the structural and electronic properties of one of the cubic SnMgCu4-type structure ternary compound, YMgNi4, recently synthesized and of its hydride YMgNi4H4. For the hydride, we predict that the Pmn2(j) structure is more stable than a cubic structure. The calculated enthalpy of formation of the hydride, -37.7 kJ/mol H-2 is in good agreement with the experimental data, -38.5 kJ/mol H-2 of Aono et al. (C) 2006 Elsevier B.V. All rights reserved.