Nuclear magnetic resonance study of the electronic structure and hydrogen diffusion in the random b.c.c. VyTa1−y-H(D) system

Pulsed-field-gradient NMR study of hydrogen diffusivity in random b.c.c. alloys VyTa1−y

“…host-metal lattice and the lattice parameters a = 3.278, 3.188 and 3.112Å for y = 0.25, 0.50 and 0.75, respectively. According to the results of previous studies [10], these samples retain the single-phase state down to 100 K.…”

“…Nuclear magnetic resonance (NMR) measurements of the proton spin-lattice relaxation rates R 1 in b.c.c. V y Nb 1−y H 0.2 [7] and V y Ta 1−y H x [9,10] have confirmed high hydrogen mobility in these systems. However, such relaxation rate measurements cannot give a direct information on the diffusion coefficient of hydrogen.…”

“…It is interesting to compare the results of the present D measurements for V y Ta 1−y H 0.07 with the proton spin-lattice relaxation data [10] for the samples of the same composition. The R 1 data for V y Ta 1−y H x [10] have been interpreted in terms of the Bloembergen-Purcell-Pound (BPP) model [17] with a Gaussian distribution of activation energies for the H jump rate. The values of the average activation energiesĒ a derived from the R 1 data are 0.22 eV for V 0.25 Ta 0.75 H 0.07 , 0.20 eV for V 0.50 Ta 0.50 H 0.07 and 0.09 eV for V 0.75 Ta 0.25 H 0.07 [10].…”

“…[10]. In order to study the effect of host-alloy composition on the hydrogen diffusivity at relatively small H concentrations, we have chosen three samples with the same H content (x = 0.07), but with different V contents (y = 0.25, 0.50 and 0.75).…”

“…However, such relaxation rate measurements cannot give a direct information on the diffusion coefficient of hydrogen. Furthermore, because of the presence of substantial low-temperature contributions to R 1 due to conduction electrons and cross-relaxation processes [10], the relaxation rate measurements can hardly be used to search for possible deviations [1][2][3] from the Arrhenius behavior of H mobility. The pulsed-field-gradient (PFG) spin-echo NMR technique [11] permits direct measurements of the long-range diffusivity D. This technique has been successfully applied to measure the hydrogen diffusivity in the b.c.c.…”