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Zusammenfassung:
The deuteron spin-lattice relaxation in the substoichiometric dideuterides HfDx(1.68<~x<~1.90) and TiDx(x=1.91) has been measured at temperatures between 300 and 830 K. The results are compared with previous proton NMR measurements on dihydrides of similar hydrogen contents. The deuteron relaxation rate Γ1, which consists of quadrupolar (Γ1,quad), dipolar (Γ1,dip), and electronic (Γ1,e) contributions, is dominated by Γ1,quad. The deuterium atoms jump predominantly from occupied tetrahedral sites (T sites) to nearest-neighbor vacant T sites. The fluctuations in the electric field gradients are related to the jumps of the vacancies on the deuterium sublattice. The Γ1,quad maximum occurs at a lower temperature than the Γ1,dip maximum, reflecting the higher jump frequency of the vacancies compared to that of the deuterium atoms. The temperature dependence of Γ1,quad yields the activation enthalpy Ha of the deuterium vacancies and thus that of the deuterium atoms in the dideuterides. These Ha values are in good agreement with the activation enthalpies of hydrogen atoms in corresponding dihydrides.
