Early $\beta$-NMR investigations in GaAs and Ge

In this paper, we describe initial studies of the structure and dynamics associated with Li + 8 in bulk crystalline GaAs and Ge. At low temperatures in GaAs, the amplitude of the Li + 8 resonance signal at ≈ 3 T indicates that a large fraction (at least 70 % ) of the Li end up in locations with cubic symmetry (i.e. the tetrahedral interstitial and substitutional sites). The linewidth of the β -NMR Li + 8 resonance increases dramatically above 150 K, reaches a maximum at about 290 K, and decreases again. This suggests that the Li starts to change its location, probably from an interstitial to a substitutional site, at ≈ 150 K . Experiments in Ge are also described. In this sample, a narrow resonance is seen at low temperatures that is likely due to Li located at an interstitial site. Near room temperature, it appears that Li is converting to another site.