Siting and Mobility of Deuterium Absorbed in Cosputtered Mg0.65Ti0.35. A MAS 2H NMR Study

Nanostructured magnesium titanium alloys are interesting lightweight materials for chemical hydrogen storage. We have therefore investigated the siting and dynamics of deuterium absorbed in a Mg 0.65 Ti 0.35 alloy generated by magnetron cosputtering, and made a comparison to the corresponding features in bulk samples of deuterium-loaded Mg 0.65 Ti 0.35 and Mg 0.65 Sc 0.35 prepared by ball-milling and melt-casting, respectively. Magic-angle spinning 2 H NMR of cosputtered Mg 0.65 Ti 0.35 D 1.1 shows partly resolved signals of deuterium located in nonconductive domains at tetrahedral Mg 4 and mixed Mg n Ti 4− n sites (4 ppm) and deuterium at Ti 4 sites in conducting TiD 2 nanodomains (−29 and −68 ppm). No bulk TiD 2 signal at −150 ppm is observed, in contrast to what we find in ball-milled Mg 0.65 Ti 0.35 D 0.65, which is largely phase separated. The deuterium species with shift values of 4 and −29 ppm undergo complete exchange at a subsecond time scale in one- and two-dimensional exchange NMR and must therefore be close together in the lattice. In contrast, deuterium resonating at −68 ppm does not show deuterium exchange and thus appears to be located at more stable sites. The observed deuterium exchange and the reduced Knight shift compared to bulk TiD 2 are explained using a model with TiD 2 nanoslabs.