Mihoko Okui

Photoelectrochemical study of hydrogen in zirconium oxide

Abstract The chemical states of hydrogen in a zirconium oxide film were studied by photoelectrochemical (PEC) measurements and electrochemical impedance spectroscopy (EIS) measurements. The oxide films were prepared by the oxidation of a zirconium sheet (purity 99.7%) in air at 673 K for 18 h. In order to obtain a hydrogen-implanted oxide film, the oxide film was implanted with 100 keV H + ions to a dose of 10 17 cm −2 at room temperature. From the PEC measurements, the band gap energy for the hydrogen-free oxide film was determined to be about 4.8 eV and it was reduced to 3.5 eV by hydrogen implantation. The distribution of the carrier density in the band gap was obtained by EIS measurements using Mott–Schottky analysis. Hydrogen implanted into the oxide film caused the impurity level in the original band gap. This result was consistent with that of PEC measurements.

Electronic states of hydrogen in zirconium oxide

Abstract First-principles molecular orbital calculations for the electronic states of hydrogen in ZrO 2 have been carried out using the discrete variational-Xα cluster method. Both the band gap energy and the valence band structure of ZrO 2 are in good agreement with experimental results. By the introduction of a hydrogen atom, a new impurity level appears below the conduction band and the band gap is greatly reduced. Calculated partial density of states of the H 1s component in the band gap reproduces the experimental results obtained by means of Mott–Schottky analysis. The dominant chemical bond in ZrO 2 is found to be the strong ionic bond between Zr and O atoms, and the bonding character is hardly modified by the hydrogen content.

Nanoindentation of zirconium oxide films prepared near the α/β transformation temperature

Zirconium oxidized above the α/β transformation temperature and quenched to room temperature, had a needle-like prior-β phase. As prior-β zirconium was known to influence the mechanical properties of the cladding tube during a loss-of-coolant accident (LOCA), the nanochemical properties of prior-β zirconium were studied by nanoindentation tests at room temperature. The nanohardness and the oxygen distribution of prior-β phase have wave undulations whose wavelengths are almost the same as the grain size in the prior-β phase. A grain in the prior-β phase has nanohardness distribution caused by the difference in oxygen concentration.