Change of chemical states of niobium in the oxide layer of zirconium-niobium alloys with oxide growth

The change of chemical states of niobium with oxide growth was examined in the oxide layers of Zr-2.5Nb around the first kinetic transition by the conversion electron yield -X-ray absorption near-edge structure measurements. The detailed depth profiles of niobium chemical states were obtained in both the pre-and the post-transition oxide layers of Zr-2.5Nb formed in water at 663 K for 40-280 d. The depth profiling revealed that the inner oxide layer remained protective to oxidizing species even though in the post-transition region and this excellent stability of barrierness would be attributed the suppression of hydrogen pickup.