Diffuse reflectance and X-ray photoelectron spectroscopy of uranium in ZrO2 and Y2Ti2O7

Diffuse reflectance measurements were made over the wavenumber range of 4000–20,000 cm−1 at room temperature on monoclinic and stabilised ZrO2, together with Y2Ti2O7 having the pyrochlore structure, all of which were doped with U and sintered in various atmospheres. X-ray photoelectron spectroscopy measurements were also carried out on selected samples. In monoclinic and stabilised zirconia, U exhibited valence states of +4 and/or +5, depending on the sintering atmosphere and the presence of appropriate charge compensators. Using both diffuse reflectance and X-ray photoelectron spectroscopy, U was also observed as mainly U4+ and/or U5+ in U-doped Y2Ti2O7 sintered at 1400 °C in air or Ar, although a small amount of U6+ also appeared to be present in some U-doped Y2Ti2O7 samples heated in air.