Effect of Mg/Ni ratio on microstructure of Mg-Ni films deposited by magnetron sputtering

The relationship between the Mg/Ni ratio and microstructure of Mg-Ni films with a Pd-cap deposited by magnetron sputtering is investigated using transmission electron microscopy. As a result, the 6Mg-Ni films are observed to be composed of a Mg-rich amorphous matrix and Mg₂Ni nanocrystals. In contrast, the 10Mg-Ni films contain Mg nanocrystals and Mg-rich amorphous. The 2Mg-Ni films, which absorb/desorb hydrogen repeatedly as well as 6Mg-Ni films, are fully amorphous and have a homogeneous distribution of Mg and Ni. The hydrogenated 6Mg-Ni film, after 200 cycles of hydrogenation/dehydrogenation, includes Mg₂NiH₄ and MgH₂ nanocrystals as well as Mg crystals. In conclusion, the crystallization of Mg reduces desorption kinetics and cycle ability of the Mg-Ni films. Our results suggested that Mg crystallization occurs in films with an initial Mg/Ni ratio greater than 7.7 the eutectic composition between Mg and Mg₂Ni.