NUCLEAR-MAGNETIC-RESONANCE STUDIES OF HYDROGEN DIFFUSION IN THE LAYER-STRUCTURED SYSTEM ZRCLHX

Citation
M. Stoll et al., NUCLEAR-MAGNETIC-RESONANCE STUDIES OF HYDROGEN DIFFUSION IN THE LAYER-STRUCTURED SYSTEM ZRCLHX, Journal of alloys and compounds, 253, 1997, pp. 435-440
Citations number
27
Categorie Soggetti
Chemistry Physical","Metallurgy & Metallurigical Engineering","Material Science
ISSN journal
09258388
Volume
253
Year of publication
1997
Pages
435 - 440
Database
ISI
SICI code
0925-8388(1997)253:<435:NSOHDI>2.0.ZU;2-M
Abstract
The proton spin-lattice relaxation rate Gamma(1) in ZrClH0.5 shows one maximum and two shoulders, which indicates three distinct modes of hy drogen motion. The frequency dependence of the spin-lattice relaxation rate in the rotating frame, Gamma(1,rho), shows clearly that hydrogen diffusion is confined to two dimensions. Direct measurements of the l ong-range diffusivity D-xy were performed by pulsed field gradient (PF G) spin-echo NMR. These PFG experiments confirmed the two-dimensional character of hydrogen diffusion. The temperature dependence of D-xy yi elds an activation enthalpy, H-a=0.49 eV, which is in good agreement w ith the value H-a=0.47 eV deduced from the frequency-dependent Gamma(1 ,rho) data. The different processes of hydrogen motion are discussed o n an atomistic scale. The Gamma(1) and Gamma(1,rho) curves measured in ZrClH1.0 are consistent with a single mechanism of hydrogen diffusion . Both the relaxation data and the PFG data reveal a strongly reduced hydrogen mobility in ZrClH1.0 compared to ZrClH0.5. From the analysis of the echo amplitude in the PFC experiments it is concluded that the hydrogen diffusion is restricted to two dimensions as well. The D-xy v alues show Arrhenius behavior with an activation enthalpy of H-a=0.58 eV.