Structural evolution and chemical durability of uranium-doped high-entropy pyrochlore

The high-entropy ceramic solidified body ((LaPrEuGdYb)yUx)2Zr2O7+δ (y = (1−x)/5, x = 0.05, 0.10, 0.15, 0.20, 0.25) was prepared by immobilizing uranium (U) on the A-site of the pyrochlore in this study. The phase composition and evolution of solidified body were determined by XRD, Raman and SEM analysis. The phase of (LaPrEuGdYb)yUx)2Zr2O7+δ ceramic was varied with U doping amounts: a dual-phase of pyrochlore and fluorite with no U doping. A single-phase pyrochlore with U doping amounts from x = 0.15 to x = 0.20, and the U3O8 phase was precipitated at doping levels above x = 0.25. The solid solution limit for high entropy pyrochlore in relation to uranium is roughly x = 0.2. The results should be linked to the increase in configurational entropy and the variation of U valence in the ceramic bodies, as evidenced by XPS. The normalized leaching rate of U from high-entropy ceramic waste forms (x = 0.20) was about 1.65 × 10−5 g/m2⋅d after 42 d leaching. It performed well in the leaching tests. Our study is expected to provide candidate materials for solidifying complex high-level radioactive waste (HLW).