HYDROGEN DIFFUSION AND ELECTRONIC-STRUCTURE PARAMETERS IN TANTALUM HYDRIDES DETERMINED BY PULSED NMR MEASUREMENTS

Measurements are reported of the proton spin-lattice relaxation time, in the tantalumhydrogen system over the temperature and composition ranges, 77 ≤T≤470 and 0.155≤ H/Ta ≤ 0.677, respectively. In the high temperature, solid-solution (α) phase, the activation energy for hydrogen diffusion determined from the dipolar contribution to T1, shows a weakly increasing trend from 0.134 eV/atom at H/Ta = 0.155 to 0.140 eV/atom at H/Ta = 0.677.Boundaries between ordered hydride phases and the phase, located by the occurrence of abrupt changes in T1, agree very well with other recent determinations. The quantity (T1eT)-1/2, based on the conduction electron contribution, (T1e)-1, to the relaxation rate (T1);-1, is proportional to the density of states at the Fermi level N(EF). (T1e)-1/2 decreases linearly with increasing hydrogen concentration, similarly to its behavior in the V-H and Nb-Hsystems. © by Akademische Verlagsgesellschaft