Morphology and microstructure of Mg-Ti-H films deposited by microwave plasma-assisted co-sputtering

Mg-Ti-H films with a Ti content in the range 0 ≤ at.% Ti < 20 were obtained in a single-step process using the microwave reactive plasma-assisted co-sputtering technique. The morphology, crystal structure, chemical composition and spatial distribution of the elements were investigated by X-ray diffraction, scanning and transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and precession electron diffraction. Our results show that the Ti-poor films (0 ≤ at.% Ti ≤ 0.45) exhibit mainly the tetragonal β-MgH2 phase and have a dense microstructure with discontinuous columnar grains. For the films with a medium Ti content (2.7 ≤ at.% Ti ≤ 6.6), the β-MgH2, metastable orthorhombic γ-MgH2 and Mg-Ti phases were found in different proportions, with a typical columnar growth. The abrupt microstructural changes of the films with a Ti content >10 at.% correlate with the change in crystallinity. These films exhibit a mainly amorphous/nanocrystalline structure with a granular morphology. We showed that the Ti content plays a significant role in the formation of structural and microstructural features of the Mg-Ti-H films, which might be a useful parameter in tuning the functional properties of magnesium hydride.