Synthesis, microstructures, and aqueous chemical durability of high-entropy pyrochlore ceramic Eu2B2O7 (BTi, Zr, Sn, Hf, Nb, and Ce) for nuclear waste immobilization

High-entropy pyrochlore ceramics with the nominal composition Eu 2 B 2 O 7 , incorporating up to five equiatomic B-site cations, were synthesized via a solid-state reaction method and evaluated their aqueous chemical durability for nuclear waste immobilization. Comprehensive characterization using XRD, Raman, and SEM analyses confirmed the formation of a single-phase pyrochlore structure with uniform and random elemental distribution. However, secondary phases were observed in the Ce- and Nb-doped samples, which is attributed to the larger ionic radius of Ce and the higher valence state of Nb. The 42 days leaching tests revealed normalized element release rates ranging from 10 −5 to 10 −7 g/(m 2 ∙d), significantly lower than those of conventional pyrochlore materials. This enhanced durability is attributed to synergistic effects of electronegativity, ionic radius, and atomic number, which together hinder cation diffusion and strengthen chemical durability at the B site. These findings demonstrate the potential of Eu 2 B 2 O 7 high-entropy pyrochlore ceramics as long-term host materials for high-level radioactive waste. This study provides a valuable resource for enriching the thermophysical properties database of B-site high-entropy pyrochlore solidification, thereby supporting their engineering development.