Room-temperature protonic conduction in nanocrystalline films of yttria-stabilized zirconia

We report the results of our investigation on protonic conduction in 1 mu m-thick polycrystalline films of 8 mol% yttria-stabilized zirconia (YSZ) with an average grain size of 17 nm prepared on sapphire substrate using a spin-coating process. Protonic conductivity of the films is found to be higher by over an order of magnitude (at 30 degrees C) than earlier reported values for nanocrystalline YSZ bulk ceramics with a similar grain size. This value is comparable to the oxygen-ionic conductivity of this material presented at about 400 degrees C. These results suggest that, besides grain size, the structural characteristics of the grain boundaries may also play an important role in determining protonic transport in this material, and possibly other nanocrystalline solid electrolytes (SEs), and that the protonic conductivity can further be enhanced by optimizing such characteristics of the grain boundaries.