${\mathrm{MgH}}_2$ is a promising compound for hydrogen storage. Its relatively high stability has been the main obstacle for practical applications. Here, first-principles calculations of ${\mathrm{MgH}}_2$ and ${\mathrm{MgH}}_2-X$ $(X=\mathrm{Al},$ Ti, Fe, Ni, Cu, or Nb) were carried out to investigate the influences of selected alloying elements on the stability of the magnesium hydride. The full-potential linearized augmented plane-wave method within the generalized gradient approximation was used in the present study. The influence of alloying elements on the stability of magnesium dihydride was investigated through calculations of the total energy of the considered systems. It was shown that the alloying elements considered here decrease the heat of formation of $(\mathrm{Mg},X){\mathrm{H}}_2$—i.e., destabilizing the hydride—with decreasing order of effect from Cu, Ni, Al, Nb, and Fe to Ti. The destabilization of the magnesium hydride by the alloying elements was due to a weakened bonding between magnesium and hydrogen atoms. Hence, the dehydrogenation properties of ${\mathrm{MgH}}_2$ are expected to be improved to a different extent by the addition of alloying elements.

• Received 25 March 2003

DOI:https://doi.org/10.1103/PhysRevB.69.094205