Diffuse reflectance spectroscopy of Np and Pu in zirconia and pyrochlore-structured Y2Ti2O7

Diffuse reflectance spectroscopy (DRS) measurements were made over the wavenumber range of 4000–20,000 cm−1 at room temperature on monoclinic and stabilized zirconia and pyrochlore-structured Y2Ti2O7, which were doped with Np or Pu and sintered at ∼1400 °C in various atmospheres. Np4+ was present in uncompensated monoclinic zirconia samples sintered in air, Ar or H2/N2. Np6+ was obtained in air/Ar-sintered monoclinic zirconia that also contained Y3+ as charge compensators, and Np4+ was formed on sintering in H2/N2. Np4+ was present in Y-stabilized zirconia after firing in air, Ar or H2/N2. Pu4+ was observed in air-fired Pu-doped monoclinic zirconia, and sintering in Ar or H2/N2 produced Pu3+ while only Pu4+ was identified in Y-stabilized zirconia sintered in air, Ar or H2/N2. Only Pu4+ and Np4+ were observed in Y2Ti2O7 after sintering in air or argon, even when Ca was substituted for Y to try to encourage the formation of higher valence states of Pu and Np.