Significantly enhanced ionic conductivity of yttria-stabilized zirconia polycrystalline nano-film by thermal annealing

• Polycrystalline yttria-stabilized zirconia nano-films were made by sputtering.
• Ionic conductivities of such films were enhanced by thermal annealing.
• Thermal annealing switched residual stress from compressive to tensile.
• Interface conduction was observed in these nano-films.

Cubic yttria-stabilized zirconia (YSZ) polycrystalline films were fabricated onto quartz insulator substrates by reactive pulsed-DC magnetron sputtering using Zr–Y targets. The ionic conductivity of the as-deposited YSZ nano-film could be improved by annealing. The ionic conductivity of the annealed 30-nm YSZ film, 0.41 S/cm, is twenty seven times higher than that of the bulk YSZ specimen, 0.015 S/cm, when both are measured at 800 °C. In addition, the ionic conductivity of YSZ polycrystalline nano-film was found to increase with decreasing film thickness, showing that it is an interface controlled process. Thermal annealing was found to eliminate the dislocations formed during sputtering as well as to enhance the film crystallinity.