Deposition, structure, and properties of cermet thin films composed of Ag and Y-stabilized zirconia

This paper reports that Ag1-x[(Y2O3)0.1(ZrO2)0.9]x (YSZ) cermet thin films have been deposited by reactive magnetron cosputtering from Ag and Zr/Y targets in Ar-O2 mixtures. The deposition conditions were such that the YSZ component in the films was fully oxidized. The film densities varied from ∼75% to >85% as the total pressure was decreased from 20 to 5 mTorr. Film resistivities ρ varied with Ag volume fraction fAg from 5 x 10-6 Ω-cm to >109 Ω-cm. For fAg < 0.4, ρ decreased rapidly with increasing fAg. For fAg > 0.4, ρ decreased more gradually with increasing fAg. ρ in annealed films ranged from 4 x 10-4 Ω-cm for fAg = 0.4 to 5 x 10-6 Ω-cm for pure Ag. Long term (>100 h) annealing at ≥700 degrees C resulted in a gradual increase in cermet resistivity due to Ag evaporation and Ag segregation to surface islands. Both decomposition mechanisms were effectively suppressed due to Ag evaporation and Ag segregation to surface islands. Both decomposition mechanisms were effectively suppressed at up to 750 degrees C by depositing a 1 μm thick porous perovskite cap layer on the cermet. Complex impedance spectroscopy measurements in air of cermet electrodes on YSZ electrolytes gave interfacial resistances that were a factor of ∼6 lower than those of pure AG electrodes, e.g., 1.4 Ω-cm2 at 750 degrees C. Ag-YSZ cermets thus have potential as high-conductivity, low-overpotential air electrode materials for solid-oxide electrochemical devices operating at temperatures ≤750 degrees C