  We report on the stability and magnetic state of ion implanted $^8$Li in
single crystals of the semiconductor ZnO using $\beta$-detected nuclear
magnetic resonance. At ultradilute concentrations, the spectra reveal distinct
Li sites from 7.6 to 400 K. Ionized shallow donor interstitial Li is stable
across the entire temperature range, confirming its ability to self-compensate
the acceptor character of its (Zn) substitutional counterpart. Above 300 K,
spin-lattice relaxation indicates the onset of correlated local motion of
interacting defects, and the spectra show a site change transition from
disordered configurations to substitutional. Like the interstitial, the
substitutional shows no resolved hyperfine splitting, indicating it is also
fully ionized above 210 K. The electric field gradient at the interstitial
$^8$Li exhibits substantial temperature dependence with a power law typical of
non-cubic metals.
