Observing Local Oxygen Interstitial Diffusion in Donor-Doped Ceria by 17O NMR Relaxometry

The local structure and oxygen ion dynamics in pure CeO2 and CeO2 doped with Ta and Gd is studied by 17O nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy, and conductivity measurements. 17O magic-angle spinning nuclear magnetic resonance spectra of CeO2 doped with Ta show two oxygen environments. A major peak at 876 ppm represents the oxygen ions on the regular crystal lattice site with four Ce4+ neighbors. A second small peak at 751 ppm (1–2% area fraction) represents point defects that can be ascribed to interstitial oxygen ions. The concentration of these point defects increases with the dopant concentration. Oxygen ion dynamics was studied by variable-temperature spin–lattice relaxation time measurements on pure and Ta-doped CeO2 powders. The obtained results reveal a fast local jump process in Ta-doped CeO2 with a jump rate of about 2.5·108 s–1 at 350 K. This local hopping process is assigned to interstitial oxygen ions trapped by tantalum dopand ions.