First-principles investigation of Mg2Ni phase and high/low temperature Mg2NiH4 complex hydrides

Using a density functional approach calculation, the structural, energetic and electronic properties of Mg2Ni phase as well as its high/low temperature (HT/LT)-Mg2NiH4 complex hydricles are systematically investigated. The optimized structural parameters including lattice constants and atomic positions are very close to the experimental data determined from X-ray and neutron powder diffraction. A detailed study of the electronic structures including the energy band, density of states (DOS) and charge density distribution reveals the orbital hybridization and characteristics of bonding orbits within Mg2Ni and its hydrides. Based on the calculated results of the reaction heat of hydrogenation, enthalpy of formation and energy cost to remove H atoms, it is found that the formation ability of LT-Mg2NiH4 is higher than that of the HT phase during the hydrogenation of Mg2Ni alloy: moreover, LT-Mg2NiH4 has a relatively higher structural stability than HT phase, which is also well explained through the DOS and the charge distributions of HT/LT-Mg2NiH4 phases. (C) 2008 Elsevier Ltd. All rights reserved.