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 rA to rB of high-entropy pyrochlore Gd2(Ti0.25Zr0.25Hf0.25Ce0.25)2O7 is 1.4499, this one observation suggests that for high-entropy pyrochlore, the rA/rB limit of pyrochlore phase is different from that of single-component pyrochlore (1.46 < rA/rB < 1.78). In order to evaluate the radiation resistance of high-entropy pyrochlores, four typical samples were irradiated by 800 keV Kr2+ 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 (Sm0.5Gd0.5)2(Ti0.25Zr0.25Hf0.25Ce0.25)2O7 and (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2(Ti0.25Zr0.25Hf0.25Ce0.25)2O7, phase separation appears after irradiation. The results from the first principles calculations confirm that Gd2(Ti0.25Zr0.25Hf0.25Ce0.25)2O7 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.