Dense CeO2 layers of 350nm thickness, with columnar grains of size 25nm, were radio-frequency sputtered on silicon. 18O isotope exchange in the temperature range from 200 to 575C showed surface exchange at CeO2 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:

ks(cm/s) = 2.7 x 10-8exp[-0.3(eV)/kT]

or

kgb(cm/s) = 10-9exp[-0.3(eV)/kT]

A 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 to be 10−15cm2/s at 575C.

Fast Ion Transport in Nanoscaled Thin Film Cerium Oxide. S.Swaroop, M.Kilo, A.E.Kossoy, I.Lubomirsky, I.Riess: Solid State Ionics, 2008, 179[21-26], 1205-8