Mg-Ti nanostructured samples with different Ti contents were prepared via compaction of nanoparticles grown by inert gas condensation with independent Mg and Ti vapour sources. The growth set-up offered the option to perform in situ hydrogen absorption before compaction. Structural and morphological characterisation was carried out by X-ray diffraction, energy dispersive spectroscopy and electron microscopy. The formation of an extended metastable solid solution of Ti in hcp Mg was detected up to 15 at% Ti in the as-grown nanoparticles, while after in situ hydrogen absorption, phase separation between MgH2 and TiH2 was observed. At a Ti content of 22 at%, a metastable Mg-Ti-H fcc phase was observed after in situ hydrogen absorption. The co-evaporation of Mg and Ti inhibited nanoparticle coalescence and crystallite growth in comparison with the evaporation of Mg only. In situ hydrogen absorption was beneficial to subsequent hydrogen behaviour, studied by high pressure differential scanning calorimetry and isothermal kinetics. A transformed fraction of 90% was reached within 100 s at 300 °C during both hydrogen absorption and desorption. The enthalpy of hydride formation was not observed to differ from bulk MgH2.

Structural properties and reversible deuterium uptake of MgD 2 −TiD 2 nanocomposites have been studied by joint X-ray and neutron diffraction analyses to shed light on the extremely fast hydrogenation kinetics of these materials. (1 − x)MgD 2 −xTiD 2 nanocomposites with compositions ranging between x = 0 and 0.5 have been prepared by reactive ball milling of Mg and Ti powders under deuterium pressure. They consist of mixtures of MgD 2 (β-and γ-polymorphs) and ε-TiD 2 phases homogenously distributed at the nanoscale with crystallite sizes below 15 nm. Minor phase miscibility is detected with Mg solubility in the TiD 2 phase up to 8 at.% and Ti solubility in the β-MgD 2 up to 7 at.% Ti. At moderate temperatures and pressures (T < 600 K, P D2 < 1 MPa) reversible deuterium loading in MgD 2 −TiD 2 nanocomposites only occurs through the β-MgD 2 to Mg transformation. Mg/MgD 2 thermodynamics is not modified as γ-MgD 2 and Ti solubility in β-MgD 2 are metastable and do not operate during reversible deuterium loading. However, the TiD 2 phase allows for outstanding D-sorption kinetics in the Mg/MgD 2 system. This paper demonstrates that TiD 2 inclusions limit the grain growth of Mg and MgD 2 phases allowing for short D-diffusion paths. Furthermore, we provide evidence that the TiD 2 phase also favors H-mobility through the existence of coherent coupling between TiD 2 and Mg/MgD 2 phases and the presence of sub-stoichiometric MgD 2-η and TiD 2-η phases.