Structural and optical properties of MgyNi1-yHx gradient thin films in relation to the as-deposited metallic state

Thin MgyNi1-yHx, films with a gradient in chemical composition are investigated by optical spectrophotometry, dc resistivity and X-ray diffraction measurements before and after exposure to hydrogen. In the metallic state crystalline Mg2Ni is present for 0.6 <= y <= 0.8 and coexists with amorphous Mg and/or Ni. The hydride state is mainly characterized by the presence of Mg2NiH4 around the stoichiometric [Mg]/[Ni] = 2 composition and some MgH2 on the Mg-rich side. The abrupt microstructural changes found in the as-deposited metallic state around the Mg-Mg2Ni eutectic point correlate well with the compositional dependence of the optical properties in the hydride state. We conclude that the formation of the hydride depends directly on the detailed nature of the metallic parent phase. Furthermore, we demonstrate that high-throughput compositional screening via fiber-optic spectrophotometry is useful for hydride identification. When no structural long-range order is present, this provides a new tool for the search for hydrogen storage materials. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved