LAUSR

We report measurements of the dynamics of isolated 8Li+ in single crystal rutile TiO2 using β-detected nuclear magnetic resonance. From spin–lattice relaxation and motional narrowing, we find two sets of thermally activated dynamics: one below 100 K and one at higher temperatures. At low temperature, the activation barrier is 26.8(6) meV with prefactor 1.23(5) × 1010 s–1. We suggest this is unrelated to Li+ motion and rather is a consequence of electron polarons in the vicinity of the implanted 8Li+ that are known to become mobile in this temperature range. Above 100 K, Li+ undergoes long-range diffusion as an isolated uncomplexed cation, characterized by an activation energy and prefactor of 0.32(2) eV and 1.0(5) × 1016 s–1, respectively, in agreement with macroscopic diffusion measurements. These results in the dilute limit from a microscopic probe indicate that Li+ concentration does not limit the diffusivity even up to high concentrations but that some key ingredient is missing in the calculations of ...