2-DIMENSIONAL DIFFUSION OF HYDROGEN IN ZRBE2H1.4

The diffusion of hydrogen through the hexagonal metal hydride ZrBe2He1.4 has been studied by measuring the H1 nuclear spin-lattice relaxation rate T1-1 as a function of frequency and temperature. At high temperatures, where the hopping rate of the H interstitials is faster than the nuclear magnetic resonance (NMR) frequency, the relaxation rate has a frequency dependence much larger than expected for random diffusive motion in three dimensions. A previous NMR study of ZrBe2H1.4 did not account for the anomalous frequency dependence. Our data more fully define the frequency dependence, and we find that it is consistent with a model in which the motion of the hydrogen is restricted to two dimensions. Two-dimensional motion allows a self-consistent analysis of the T1-1 data for all the measured frequencies and provides an improved measure of the activation energy, Ea=0.27±0.02 eV. ZrBe2H1.4 is a metal hydride in which the frequency dependence of T1-1 indicates two-dimensional motion. © 1995 The American Physical Society.