Oxygen Transport in Sc-Doped CeO₂: Cation (⁴⁵Sc) NMR as a Probe of Anionic Conductivity^†

Oxygen-vacancy hopping dynamics in Sc-doped CeO2, a solid electrolyte (SE), was studied employing high-temperature (up to 600 degrees C) Sc-45 nuclear magnetic resonance (NMR) and electrochemical impedance spectroscopy (ETS) techniques. The oxygen vacancy hopping frequency and its temperature dependence, as obtained from the simulation of (SC)-S-45 line shapes, are in excellent agreement with those obtained from EIS. The characteristic length scale of the vacancy hopping is found to be controlled by the average Sc-Sc separation in the lattice. Moreover, direct spectroscopic evidence for the presence of small but Significant dynamical heterogeneities is observed, implying that all vacancies are not characterized by similar dynamic properties. These results clearly demonstrate that cation NMR can serve as a unique probe for anionic transport in SEs.