Diffusion processes in solid Li-Mg and Li-Ag alloys and the spin-lattice relaxation of8Li

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Abstract
The spin-lattice relaxation (SLR) of polarised radioactive 8Li nuclei in solid Li-based alloys containing 2-11 at.% Mg and 1.6-10 at.% Ag was measured via their asymmetric beta -decay radiation. For temperatures T<200K SLR is due to conduction electrons only, and the Korringa relation is found to hold in the concentration range covered. For T=200-450K, SLR is additionally influenced by atomic diffusion. The diffusional contribution consists of a dipolar part as in pure Li and a quadrupolar part induced by the solute ions. The analysis is based on the concept of two-exponential SLR for spin I=2. In Li-Mg the self-diffusion of Li and the diffusion of the solute ions are found to be slowed down on alloying. The ratio of the jump rates of Li and Mg appears to be determined simply by their atomic masses. In the case of the dilute alloy Li-1.6 at.% Ag, which is amenable to theoretical diffusion models, comparison with tracer results favours an interstitial-vacancy pair mechanism. In the framework of this model Ag is found to diffuse faster than Li.