Alloying effects of transition metals on chemical bonding in magnesium hydride MgH2 Original Research Article

By use of the first-principles density functional theory for a cluster model, the alloying effect of transition element M on the electronic structure of magnesium hydride, MgH2, is investigated. It is found that the chemical interaction between Mg and H may play a dominant role in the pure MgH2 system. Such a strong interaction remains in the alloyed Mg(M)H2 when the central Mg is replaced by an alloying element M. By a satisfactory fit of the calculated M (or Mg)–H interactions with the enthalpies of formation for some pure dihydrides, we have found that 70% chemical (ionic plus covalent) interactions would appear to be ionic but the covalent interaction of an adjacent Mg to M with a H atom around it would be sensitive to the substitution of M. It is also found that in Mg(M)H2 some weaker hydride forming elements than Mg would form a little stronger bonds with hydrogen than Mg–H bond in MgH2. The hydride formation enthalpy difference for Mg(M)H2 alloyed by the transition element M has been calculated, by which we can know which element could be used to improve the hydriding kinetics of MgH2.