Electronic mechanism of dehydrogenation of the Mg-Ge mixture during milling under hydrogen

The energy and electronic structure of the hydride phase are calculated by using the first-principles plane-wave pseudopotential method to explain experimental results of milling of a Mg–Ge mixture under hydrogen. The electronic mechanism of dehydrogenation of the Ge alloying system is also considered. By calculating heats of formation of MgH2 and (MgGe)H2 solid solutions, it is found that the structural stability of the alloying system is reduced when a little Ge dissolves in MgH2. As the Ge content increases, Mg2Ge may be formed by the reaction: 2MgH2 + Ge ↔ Mg2Ge + 2H2, at the same time, the dehydrogenating properties of the system are improved compared with that of MgH2, but are reduced by contrast with that of (MgGe)H2 solid solutions. Based on the analysis of the densities of states (DOS) of MgH2 before and after Ge alloying, it is found that the improvement of the dehydrogenating properties of MgH2 dissolved into a little Ge is attributed to the weakened bonding between magnesium and hydrogen caused by the interactions between Ge and Mg.