Fast ion transport in nanoscaled thin film cerium oxide

Dense CeO 2 layers of 350 nm thickness, with columnar grains of size 25 nm, were RF-sputtered on silicon. 18O isotope exchange in the temperature range from 200 to 575 °C showed surface exchange at CeO 2 as the rate-determining step, while diffusion through the polycrystalline thin layer was fast. The surface exchange coefficients controlled by surface or grain boundary processes were found to be k s = 2.7 × 10 − 8 exp ( − 0.3 eV k T ) cm s − 1 or k gb = 1 × 10 − 9 exp ( − 0.3 eV k T ) cm s − 1 . Comparison with literature data on doped ceria revealed that surface exchange could be dominated by grain boundary processes. A lower limit for the diffusion coefficient was determined as 10 − 15 cm 2 s − 1 at 575 °C.