Detection of Fluorite-Structured MgD2/TiD2: Deuterium NMR

Deuterium magic-angle spinning NMR spectra of MgD2/TiD2 composites are presented. After high-energy, high-pressure ball-milling of an 80:20 Mg:Ti hydride, the material was H → D exchanged using high-pressure D2 gas. This material displayed the deuterium NMR spinning sideband pattern of the MgD2 component that is typical of rutile-structured MgD2. After heat treatment at 450 °C under high D2 pressure, the sidebands became much weaker, indicating that most D atoms were now in sites of local cubic symmetry. This is in agreement with a previous proposal of a nearly fully Mg–Ti segregated, lattice coherent fluorite (fcc) structure of the composite. Because H­(D) diffusion is expected to be more rapid in the fluorite structure, compared to the rutile form, this may be important to the kinetics of hydrogen storage and release from MgH2/TiH2 composites.