Enhanced ionic conductivity and phase meta-stability of nano-sized thin film yttria-doped zirconia (YDZ)

Yttria-doped zirconia (YDZ) thin films with nanometric sized grains were prepared by reactive RF sputtering and their oxygen ion conductivities were systematically measured as a function of yttria doping with levels in the range 0.5–9.1 mol.% Y2O3. Enhanced oxygen ion conductivities, as derived from impedance spectra, were observed when compared with values reported for bulk YSZ. Furthermore, the peak conductivity for the YDZ films was observed to occur at considerably reduced yttria levels, i.e., at 6.5 mol.% Y2O3 (for T > ∼400 °C) and at 3.2 mol.% Y2O3 (for T < ∼300 °C) vs. 9 mol.% Y2O3 in bulk YSZ. Based on an analysis of the Raman spectra, these results are believed to result from the extended meta-stability of the cubic phase to reduced yttria levels at nanometric grain sizes.