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Abstract: Diffuse reflectance spectra at room temperature have been collected on polycrystalline perovskite (CaTiO3), zirconolite (CaZrTi2O7) and thorutite (ThTi2O6) samples doped with Np. The Np species give rise to a number of broad, unresolved intraconfigurational f–f electronic transition bands in the near-infrared and visible spectral regions. Both Np3+ and Np4+ can substitute in the Ca site of perovskite by the appropriate choice of charge compensation and sintering atmosphere. No detectable spectral differences were observed when Np4+ was targeted towards either the Ca or Zr sites in zirconolite. Np4+ but not Np5+ can be incorporated in the Th site of thorutite by sintering in air. Even in the most dilute [≤0.03 formula units (f.u.)] Np4+ samples of the different titanates studied, there was only very approximate agreement with the Kubelka–Munk law. [Copyright &y& Elsevier]

Highlights: [•] The incorporation of neptunium (Np) and plutonium (Pu) in thorutite (ThTi2O6) has been studied. [•] The effect of Np/Pu doping on the unit cell parameter changes has been discussed from the structure point of view. [•] The effect of Y as charge compensator to encourage the formation of higher valences of Np and Pu has been explored. [•] The resulting Np/Pu doped thorutite samples have been characterised by using XRD, SEM and DRS. [ABSTRACT FROM AUTHOR]