Nuclear relaxation in the dideuteride of hafnium and titanium

The deuteron spin-lattice relaxation in the substoichiometric dideuterides HfD x (1.68≤x≤1.90) and TiD x (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 Γ 1 , which consists of quadrupolar (Γ 1 , q u a d ), dipolar (Γ 1 , d i p ), and electronic (Γ 1 , e ) contributions, is dominated by Γ 1 , q u a d . 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 Γ 1 , q u a d maximum occurs at a lower temperature than the Γ 1 , d i p maximum, reflecting the higher jump frequency of the vacancies compared to that of the deuterium atoms. The temperature dependence of Γ 1 , q u a d yields the activation enthalpy H a of the deuterium vacancies and thus that of the deuterium atoms in the dideuterides. These H a values are in good agreement with the activation enthalpies of hydrogen atoms in corresponding dihydrides.