Influence of Compositional Complexity on Amorphization Resistance of Swift Heavy Ion Irradiated Titanate Pyrochlores

Compositionally complex oxides have garnered attention recently for their potential technological applications in harsh environments such as thermal barrier coatings and nuclear waste forms. Therefore, their response to extreme conditions, including high temperature and intense irradiation fields, must be thoroughly investigated. Here, the structural evolution of two pyrochlore oxides with comparable cation size ratio, r_A/r_B, (Yb_0.2Er_0.2Dy_0.2Tb_0.2Gd_0.2)₂Ti₂O₇ and Ho₂Ti₂O₇, was evaluated after irradiation with 946 MeV Au ions up to a fluence of 8 × 10¹² ions/cm² using synchrotron X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The overall radiation response is comparable for both titanate oxides and is dominated by a loss of crystallinity. When compared to a series of conventional titanate pyrochlore compositions, the amorphous track diameter of (Yb_0.2Er_0.2Dy_0.2Tb_0.2Gd_0.2)₂Ti₂O₇ is slightly larger than that of Ho₂Ti₂O₇ and more in line with the diameter of the endmember with the maximum A-site cation size (Gd₂Ti₂O₇). Density functional theory calculations suggest that this behavior may be linked to local lattice distortions and the associated energetics of cation antisite formation. TEM and Raman analyses show that a disordered, crystalline shell surrounds the amorphous ion tracks in (Yb_0.2Er_0.2Dy_0.2Tb_0.2Gd_0.2)₂Ti₂O₇, and the corresponding short-range structure resembles a weberite-type atomic arrangement.