Preparation and irradiation stability of A2B2O7 pyrochlore high-entropy ceramic for immobilization of high-level nuclear waste

The high-entropy pyrochlores have attracted increasing attention due to their ability to immobilize multiple nuclides simultaneously, compared with baseline single-component pyrochlores. In this work, nine kinds of multicomponent oxide ceramics are synthesized and eight of them exhibit a single pyrochlore phase. In addition, the ratio of r _A to r _B of high-entropy pyrochlore Gd ₂(Ti _0.25Zr _0.25Hf _0.25Ce _0.25) ₂O ₇ is 1.4499, this one observation suggests that for high-entropy pyrochlore, the r _A/r _B limit of pyrochlore phase is different from that of single-component pyrochlore (1.46 < r _A/r _B < 1.78). In order to evaluate the radiation resistance of high-entropy pyrochlores, four typical samples were irradiated by 800 keV Kr ²⁺ ions beam. The GIXRD results show that all the high-entropy pyrochlores only undergo a phase transition from an ordered pyrochlore structure to a disordered fluorite structure (O-D transition) at the highest irradiation dose (∼ 40 dpa) in this study, instead of being amorphous. For (Sm _0.5Gd _0.5) ₂(Ti _0.25Zr _0.25Hf _0.25Ce _0.25) ₂O ₇ and (La _0.2Nd _0.2Sm _0.2Eu _0.2Gd _0.2) ₂(Ti _0.25Zr _0.25Hf _0.25Ce _0.25) ₂O ₇, phase separation appears after irradiation. The results from the first principles calculations confirm that Gd ₂(Ti _0.25Zr _0.25Hf _0.25Ce _0.25) ₂O ₇ exhibits stronger radiation resistance than the corresponding single pyrochlores, which agrees with the irradiation experiment result. This study demonstrates that the high-entropy pyrochlores exhibit excellent irradiation stability and can be considered as the potential matrix material for immobilization of high-level nuclear waste.