Tuning the radiation tolerance of titanate pyrochlore via Sn-substitution: an in situ ion irradiation study of pyrochlore-glass ceramics

Abstract

The high-level radioactive waste stream resulting from the reprocessing of spent nuclear fuel compriseslong-lived actinides and processing chemical impurities. Glass-ceramics (GCs) are being proposed as a potential candidate to host the actinides and processing impurities in the crystalline and glass phases, respectively. Some of the ceramics considered for actinide immobilization are pyrochlores (Ln₂B₂O₇; Ln = lanthanides and Y, B = Ti, Sn, Zr, and Hf) and in the present study, the pyrochlore GCs (Y₂Ti_2−xSn_xO₇ and Ln₂TiSnO₇) have been synthesized and their response to ion-irradiation (600 keV Xe²⁺) has been investigated under in situ conditions using transmission electron microscopy (TEM). The primary focus of this study is the effect of Sn-substitution into the B-site of the pyrochlore structure on the radiation tolerance of these materials. With an increase in Sn-substitution, the materials become increasingly radiation tolerant as indicated by the higher ion-fluences required for amorphization. The fully Sn-substituted pyrochlore was determined to be ∼25 times and ∼78 times more radiation tolerant than its Ti-counterpart at 143 K and 298 K, respectively. Similarly, Sn-rich pyrochlores were determined to have a critical temperature (T_c) of amorphization ∼3 times lower than that of the Ti-rich materials. The improved radiation tolerance of Sn-substituted pyrochlores is a result of the interplay of structure, energetics, and the nature of the Ln–O and B–O bonds. This study has demonstrated that in terms of radiation tolerance, the stannate pyrochlore GC is an attractive candidate for HLW immobilization over titanate counterparts.