Solid solutions of uranium and thorium phosphates: Synthesis, characterization and X-ray photoelectron spectroscopy

New solid solutions of uranium-thorium phosphates based on uranium-uranyl phosphate U(UO2)(PO4)(2) and thorium phosphate-diphosphate Th-4(PO4)(4)(P2O7) were synthesized in air or under an inert atmosphere via dry and wet chemical processes. The products were characterized by means of chemical analysis, X-ray diffraction and ultraviolet-visible and infrared absorption spectroscopies. Solid solutions of uranium-uranyl-thorium phosphates U1-xThx(UO2)(PO4)(2) (with 0 less than or equal to x less than or equal to 0.6) were obtained in air by substitution of uranium (IV) by thorium. Solid solutions of thorium-uranium phosphate-diphosphate (Th1-yUy)(4)(PO4)(4)(P2O7) (with y less than or equal to 0.9) were prepared by substitution of thorium by uranium (IV) under an inert atmosphere. These new materials have been studied by XPS spectroscopy in order to verify the oxidation states of uranium and to estimate the P/U, P/Th, P/O and U/Th ratios.