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

Nuclear magnetic resonance measurements of the H-1, D-2 and V-51 spin-lattice relaxation rates and the V-51 Knight shifts in the random b.c.c. VyTa1-yHx(D-x) system (0.25 less than or equal to y less than or equal to 0.85, 0.07 less than or equal to x less than or equal to 0.4) have been performed in the temperature range 11-430 K. The relaxation data are analyzed to obtain the parameters of H(D) diffusion which is governed by a distribution of activation energies. In different y ranges the dependencies of the average activation energy (E) over bar(a) on hydrogen concentration are found to differ qualitatively. Comparison of the parameters of H and D diffusion in the samples of nearly the same composition shows that there is a distinct isotope effect: (E) over bar(a)(D)>($) over bar(a)(H). The behaviour of the density of electron states at the Fermi level as a function of y and x is discussed on the basis of the measured values of the V-51 Knight shifts and the electronic (Korringa) contributions to the spin-lattice relaxation rate. (C) 1998 Elsevier Science S.A. All rights reserved.