ON NUCLEAR MAGNETIC-RESONANCE STUDIES OF HYDROGEN DIFFUSION IN DISORDERED METAL-HYDROGEN SYSTEMS

The following characteristic features of the proton diffusional spin relaxation rates in disordered (i. e. non-stoichiometric and/or amorphous) metal-hydrogen systems are discussed. It is shown that whereas in ordered 'simple' hydrides 1n T//1 and 1n T//1// rho are symmetric about their minimal values, in disordered hydrides the low temperature slope is lower than the high temperature slope. 1n T//1 and 1nT//1// rho 'flatten off' to even lower slopes at lower temperatures. Whereas in ordered stoichiometric hydrides 1n T//2 is linear in 1/T at temperatures below the minimum in T//1 but still in the motionally narrowed region, in the disordered hydrides it is not; in some cases its slope increases at low temperatures and in others it decreases. The above-mentioned features can be analyzed in terms of a diffusion process governed by either a temperature-dependent activation energy E//a or a distribution of activation energies.