Zr4+ substitution tuned the radiation tolerance: in-situ ion irradiation study on amorphization behavior and mechanisms of pyrochlore glass-ceramics for nuclear waste forms

The glass-ceramic waste forms containing HLW require the host phases to maintain long-term stability under alpha decay damage. While B‑site Zr 4+ substitution is a well‑established way to enhance the radiation stability of the pyrochlore phase, studies on the irradiation behavior of Zr 4+ ‑substituted pyrochlore glass‑ceramics remain scarce. In this study, the irradiation behavior of Gd 2-x Ln x Ti 2-y Zr y O 7 (Ln = Nd and Y) pyrochlore glass-ceramics was investigated. In-situ 800 keV Kr 2+ irradiation was performed at room temperature. It revealed that B-site Zr 4+ substitution acts as the key factor enhancing radiation resistance, increasing the critical amorphization dose from 0.33 dpa to above 3.24 dpa (y(Zr) from 0 to 1.0). B‑site Zr 4+ substitution also dictates the evolution of amorphization process of the pyrochlore phase, shifting its primary irradiation defect accommodation mechanism from the order-disorder transition to cation anti‑site defects within the defect‑fluorite structure. Furthermore, the critical Ti: Zr ratio governs the amorphization mechanism. Compositions with low Zr content (Ti: Zr ≥ 3:1) undergo homogeneous amorphization via the nucleation and coalescence of isolated amorphous islands. For compositions with higher Zr content (Ti: Zr < 3:1), a dual mechanism operates, where outward Zr migration at interfaces triggers the formation of edge amorphous regions concurrent with conventional amorphization within the grain interior.