Chemical composition and structural evolution of Surface Passivation film in Rare Earth High-Entropy Ti-Pyrochlore

The passivation behavior of polycrystalline structural ceramics under extreme corrosion conditions is critical for future advanced energy applications, including nuclear waste immobilization. The current study investigated the chemical durability of the high-entropy pyrochlore rare earth Ti pyrochlore (HE-RE 2 Ti 2 O 7 ) by focusing on the fundamental understanding of the nexus between chemical composition and the structural evolution of the surface formation of passivation film. Results provide evidence to support that the formation of a multilayer surface passivation film enriched in both A and Ti elements is associated with a dissolution-reprecipitation mechanism, which is strongly associated to the metal-oxygen bonding strength. The formation of passivation film dominated by the synergistic effect of localized bonding environment led to dynamic transition between congruent and incongruent leaching mechanisms, and further affect the chemical durability. These findings establish a framework for designing corrosion-resistant nuclear waste forms by focusing on its surface alteration behavior through tuning the chemical composition.