Abstract
In order to study the mechanism and parameters of hydrogen diffusion in the hexagonal (C14-type) Lavesphase HfCr2, we have performed quasielastic neutron scattering (QENS) measurements inHfCr2H0.74 and nuclear magnetic resonance (NMR) measurements of the proton spin-lattice relaxation rate inHfCr2Hx (0.30≤x≤1.62) overthe temperature range 11–424 K. It is found that the diffusive motion of hydrogen in this system canbe described in terms of at least two jump processes: a fast localized H motion with the jump rateτl−1 and a slower processwith the rate τd−1 associated with H jumps leading to long-range diffusion. Inthe interval 175–400 K, the temperature dependences of bothτl−1 and τd−1 are reasonably described by an Arrhenius law. ForHfCr2H0.74 the corresponding activation energies derived from the QENS data are122 ± 7 meVfor τl−1 and148 ± 7 meVfor τd−1; theratio τd/τl at room temperature is close to 16. The long-range hydrogen mobility is found to decreasewith increasing H content.
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