Microscopic Dynamics of Li⁺in Rutile TiO₂Revealed by⁸Li β-Detected Nuclear Magnetic Resonance

We report measurements of the dynamics of isolated 8 Li + in single crystal rutile TiO 2 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) × 10 10 s –1 . We suggest this is unrelated to Li + motion and rather is a consequence of electron polarons in the vicinity of the implanted 8 Li + 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) × 10 16 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 the migration barrier. The anomalous prefactors provide further insight into both Li + and polaron motion.