An optical and electrochemical investigation of ZrO₂ thin films (from NM to MM thickness)

Zirconium dioxide thin films and yttria stabilised zirconia (YSZ) thin films prepared by various techniques were characterised by optical and electrochemical techniques. Zirconium oxide films were prepared anodically (2-250 nm) and by sputtering (0.3-3 μm). YSZ films were prepared by a CVD/EVD process (∼ 3 μm), by electrophoretic deposition (200 μm) and by tape casting (130 μm). These YSZ films are compared to single crystal YSZ. Characterization techniques include photoelectrochemistry (for the anodically prepared films), transmittance and reflectance spectroscopy, and impedance spectroscopy. From the photoelectrochemical studies, the changes in the bandgap were followed for films prepared under increasing electric fields. The transmittance and reflectance spectra yield information about the film thickness (for thin films) and for thicker films, information was collected about the relative quantity of localised states and their position in the bandgap; both for the bulk material and the surface. Impedance spectroscopy for thin films of ZrO₂ can be used to determine their dielectric properties. For thicker YSZ films at low temperatures (less than 500 K), impedance experiments were used to gain information about the intra-grain, inter-grain, and polarisation resistances.