Ab initio study of the hydrogenation properties of Mg-based binary and ternary compounds Mg_2X (X velence Ni, Si) and YMgNi_4

摘要

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 Mg_2NiH_4 is stable while Mg_2Si does not absorb hydrogen. Our results are in agreement with recent experimental data on the hydrogenation of Mg_2X phases (X velence Ni, Si, Ge, Sn) of Janot et al., as well as with studies of the role of Si in the destabilization of MgH_2 through the formation of Mg_2Si, by Vajo et al. We have also analyzed the structural and electronic properties of one of the cubic SnMgCu_4-type structure ternary compound, YMgNi_4, recently synthesized and of its hydride YMgNi_4H_4. For the hydride, we predict that the Pmn2_1 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.