Nuclear magnetic resonance studies of hydrogen motion in nanostructured Laves-phase hydrides ZrCr2Hx and TaV2Hx

In order to study the mobility of hydrogen in nanostructured Laves-phase hydrides, we have measured the proton nuclear magnetic resonance (NMR) spectra and the proton spin-lattice and spin-spin relaxation rates in two nanostructured systems prepared by ball milling: ZrCr2H3 and TaV2H1+delta. The proton NMR measurements have been performed at the resonance frequencies of 14, 23.8 and 90 MHz over the temperature ranges 11-424 K (for coarse-grained samples) and 11-384 K (for nanostructured samples). Hydrogen mobility in the ball-milled ZrCr2H3 is found to decrease strongly with increasing milling time. The experimental data suggest that this effect is related to the growth of the fraction of highly distorted intergrain regions where H mobility is much lower than in the crystalline grains. For the nanostructured TaV2H1+delta system, the ball milling is found to lead to a slight decrease in the long-range H mobility and to a suppression of the fast localized H motion in the crystalline grains.