Measurements of H diffusivity in the H-stabilized Laves-phase compound C15 Ti2HfHx (3.9 ≤ x ≤ 4.2) were performed by using the pulsed-field gradient nuclear magnetic resonance technique between 220 and 500K. The activation enthalpies for H diffusion, as obtained by fitting an Arrhenius expression to the diffusivities measured at a given H concentration, were 0.240eV (x = 3.9), 0.210eV (x = 4.0) and 0.235eV (x = 4.2). The proton spin-lattice relaxation rates were measured in the same samples over wide

temperature ranges and at different resonance frequencies. The relaxation-rate data for above about 250K were well-described by a relaxation model for jumps between tetrahedral [Ti3Hf] sites. A comparison with the pulsed-field gradient results showed that these jumps corresponded to long-range diffusion. At lower temperatures, the relaxation-rate data indicated localized motion of H; presumably within hexagons formed by 6 tetrahedral [Hf2Ti2] sites which had no effect upon the pulsed-field gradient measurements. Similar diffusion mechanisms had been observed in C15 Ti2ZrHx (where x was about 4).

NMR Studies of Hydrogen Diffusion in the Hydrogen-Stabilized Laves Phase Compound C15-HfTi2Hx. U.Eberle, G.Majer, A.V.Skripov, V.N.Kozhanov: Journal of Physics - Condensed Matter, 2002, 14[2], 153-64

 Table 3

 Diffusivity of B in Zr41Be22.5Ti14Cu12.5Ni10