CHEMICAL STATE OF HYDROGEN IN ZIRCONIUM OXIDE FILMS

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The hydrogen dissolution behavior of Zr0ィイD22ィエD2 and the influence of hydrogen on the electrical conductivity of Zr0ィイD22ィエD2 have been examined using a thermal desorption method and a impedance spectroscopy, respectively. The dependence of hydrogen solubility in Zr0ィイD22ィエD2 on the temperature was obtained and the results were analyzed on the basis of the reaction involving an interstitial hydrogen defect. The electrical conductivity of ZrOィイD22ィエD2 was found to increase with water vapor pressure, which appeared to result from interstitial proton conduction. These results enabled us to estimate the hydrogen diffusivity in Zr0ィイD22ィエD2. The chemical states of hydrogen in zirconium oxide films were examined using the photoelectrochemical measurements and discrete variational X α molecular orbital calculations. Effects of hydrogen charging on the photoelectrochemical properties of the oxides formed on pure Zr were evaluated from a photocurrent action spectrum. The distribution of electron states induced by hydrogen charging was estimated from the Mott-Schottky plots. Electronic mechanisms of hydrogen charging were studied in terms of the chemical bonding character. It is found that hydrogen causes the change in the energy level structure near the band gap and produce new electron states in the band gap.