ELECTRONIC-STRUCTURE OF INTERMETALLIC HYDRIDES - MG2FEH6 AND CA2RUH6

Two ternary metal hydrides of the family M//2M prime H//x, where M is a divalent simple or rare earth metal and M prime is a transition metal, are studied using the augmented plane wave band structure method. The nature and the relative strength of the transition metal-hydrogen, divalent metal-hydrogen and hydrogen-hydrogen interactions are inferred from our partial wave analysis of the wavefunctions at the metal and hydrogen sites. The compounds are found to be semiconductors, and the gap originates from a splitting of the transition metal M prime d bands. The t//2//g manifold, which does not interact with the H s states, forms narrow filled bands which are separated by a gap from the antibonding empty (M prime d(e//g))-(H s) states. The electronic origin of the maximum hydrogen capacity in this family of compounds is discussed.