Nuclear spin relaxation and translational diffusion in dilute alloys of lithium

Abstract

The longitudinal relaxation of the 7Li nuclear spins in dilute Li alloys containing 2.0, 4.0, 8.0 at%Mg; 1.5, 3.0 at%Cd; 1.5 and 2.75 at%Ag is measured. In all these alloys below 0 degrees C the relaxation rate T1-1=AT+B, where A and B are constants depending on composition. Above 0 degrees C T1-1 goes through a maximum typical of the diffusion dominated relaxation previously observed in pure Li. The maximum value of the relaxation rate due to the diffusion processes, T1(diff)-1, increases from 7.1 s-1 for pure Li to 9.7 s-1 for the 8 at%Mg, 12.6 s-1 for the 3 at%Cd, and 12 s-1 for the 2.75 at%Ag alloys. For the Mg and Cd alloys the increase is shown to be due to the interaction of the 7Li quadrupole moment with the time dependent electric field gradients in the alloys, and consistent with the broadening observed at low temperatures. The crease in the Ag alloys is apparently too large to be explained on the basis of the line broadening, and it is concluded that the enhanced effect may be evidence for an interstitial mode of diffusion in these alloys.