Nuclear Magnetic Resonance Study of the Electronic Structure and Hydrogen Motion in the Random BCC-TaV sub 2 --H(D) System

Nuclear magnetic resonance measurements of the exp 1 H, exp 2 D and exp 51 V spin-lattice relaxation times and Knight shifts in the random bcc-TaV sub 2 H sub x (D sub x ) system (0.1 < = x < = 2.4) have been performed over the temperature range 11-440K. The relaxation data are analysed to obtain the parameters of H(D) diffusion, which is governed by a distribution of activation energies. The long-range diffusion of H(D) in bcc-TaV sub 2 H sub x (D sub x ) is found to be much faster than in C15-type TaV sub 2 H sub x (D sub x ) with comparable H(D) contents. For all the studied samples (including those with mixed isotope composition), there is a distinct isotope effect on the average activation energy: E exp D sub a > E exp H sub a . The measured values of the Knight shifts and the electronic (Korringa) contributions to the spin-lattice relaxation rates indicate that the density of d-electron states at the Fermi level decreases with H(D) content.