An x-ray photoelectron spectroscopy investigation of the incorporation of surface oxides into bulk zirconium

X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy have been used to investigate the mechanism by which a thin ZrO2 film formed at the surface of polycrystalline zirconium dissolves into the bulk zirconium at 400 °C under nonoxidizing conditions. In addition to ZrO2, a zirconium suboxide is directly observed in the XPS spectra taken after oxidation. On heating the oxidized Zr the intensity of both the Zr 3d5/2 associated with ZrO2 and the O 1s decay linearly with time. A concomitant linear increase is observed in the summed intensities of the Zr 3d5/2 band associated with Zr metal and the suboxide ZrxO. A model is proposed to explain these observations which involves oxygen ion transport from the ZrO2 to the metal interface where formation of a suboxide intermediate appears to be the rate-controlling step. The postulated suboxide at this temperature is ZrxO with x>1.