Photocurrent spectroscopy applied to the characterization of passive films on sputter-deposited Ti–Zr alloys

A photoelectrochemical investigation on thin (⩽13 nm) mixed oxides grown on sputter-deposited Ti–Zr alloys of different composition by air exposure and by anodizing (formation voltage, UF = 4 V/SCE) was carried out. The experimental results showed that the optical band gap, Egopt, increases with increasing Zr content in both air formed and anodic films. Such behaviour is in agreement with the theoretical expectation based on the correlation between the band gap values of oxides and the difference of electronegativity of their constituents. The flat band potential of the mixed oxides was found to be almost independent on the Ti/Zr ratio into the film and more anodic with respect to those estimated for oxide grown on pure Zr. The semiconducting or insulating character of the investigated films was strongly influenced by the forming conditions and the alloy composition.