Pu-Doping-Induced Weberite-like Local Motifs and Enhanced Immobilization in Gd₂Zr₂O₇ Pyrochlore: A DFT + U Study

This study employs density functional theory with the Hubbard U correction (DFT + U) method to investigate how Pu incorporation into distinct sites (Gd or Zr) in Gd₂Zr₂O₇ governs locally weberite-like disorder and subsequently influences Pu immobilization behavior. We reveal that incorporating Pu into Zr sites induces spontaneous 48f oxygen displacement toward vacant 8a sites, forming weberite-like local motifs characterized by 7-fold coordinated Pu. This structural disorder increases the oxygen positional parameter x _O48f and elongates average Pu-O_48f bonds. Solution energies confirm preferential Pu immobilization at Zr sites, where the locally disordered weberite-like arrangement provides additional stabilization. Electronic structure analysis reveals that Pu incorporation into Zr sites induces stronger Pu-O hybridization than Gd-site substitution. Crucially, the 7-coordinated Pu in locally disordered weberite-like arrangements exhibits pronounced ionic character, which could favor Pu immobilization at Zr sites in Gd₂Zr₂O₇. These results suggest that local weberite-like disorder may be a key mechanism for optimizing Pu immobilization in pyrochlore ceramics.