Photoelectrochemical properties and band structure of oxide films on zirconium–transition metal alloys

The microalloying effects of 4d and 5d transition metals, M (M: Nb, Mo, Ta, W) on the photoelectrochemical properties, the flat band potential ( U fb ) and the band gap energy ( E g ), for zirconium oxide films were investigated by photoelectrochemical measurements and band calculation. Button ingots of zirconium–5 mol% M (M: Nb, Mo, Ta, W) were made from high-purity metals (99.9% purity) by arc melting in a purified argon atmosphere. These plate specimens were sealed into silica tubes in vacuum, and then homogenized at 1273 K for 24 h. Subsequently, these specimens were oxidized up to 1173 K. The photocurrent of each specimen was evaluated at room temperature under the irradiation of Xe lamp (500 W) through grating monochrometer and cut-off filter. 0.1 M Na 2 SO 4 solution was used as the electrolyte. The value of the flat band potential was higher and the value of the band gap energy was smaller than that of pure zirconium oxide film in all sample. It was found from the calculation by CASTEP code that the decreases in band gap energy of these oxide films was due to formation of 4d or 5d orbital of transition metals.