Deposition, Structure, and Properties of Cermet Thin Films Composed of Ag and Y-Stabilized Zirconia

Ag_1–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 p varied with Ag volume fraction f_Ag from 5 × 10^–6 Ω–cm to > 10⁹ Ω–cm. For f_Ag < 0.4, ρ decreased rapidly with increasing f_Ag. For f_Ag > 0.4, p decreased more gradually with increasing f_Ag. ρ in annealed films ranged from 4 × 10^–4 Ω–cm for f_Ag = 0.4 to 5 × 10^–6 Ω–cm for pure Ag. Long term (>100 h) annealing at ≥ 700°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 at up to 750°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, eg., 1.4 Ω–cm² at 750°C. Ag–YSZ cermets thus have potential as high–conductivity, low–overpotential air electrode materials for solid–oxide electrochemical devices operating at temperatures ≤750°C.