Photoelectrochemical characterization of thin anodic oxide films on zirconium metal

The effect of metal surface preparation on the properties of thin oxide films grown on zirconium in different electrolytes was investigated by photocurrent spectroscopy. Both passive layers grown by free corrosion of the samples in a solution and thin oxides grown anodically at a constant rate were investigated. The photoelectrochemical results give a complex picture of the interface, being influenced by the metal surface preparation, the solution pH and the electrode potential. A duplex structure of the films has been suggested on the basis of the photocurrent spectra, with an external hydrous layer (amorphous or strongly defective) having an optical gap (E(g2) similar to 3 eV) lower respect to that of the underlying anhydrous oxide (E(g1)=4.65+/-0.1 eV). The photoresponse of the hydrated phase was strongly influenced by the initial surface treatment of the base metal. Both anodic and cathodic photocurrents were recorded to the latter being originated by external (very thin films) or internal (thicker films, anodic oxides) electron photoemission phenomena which take place under cathodic polarization of the metal/oxide/electrolyte interface. Copyright (C) 1996 Elsevier Science Ltd.