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In this paper, to identify the order-disorder structure and performance of (Gd, Sm)2(Zr, Ce)2O7 ceramic as the host matrices for immobilizing actinides, various contents of Sm/Ce co-incorporated (Gd, Sm)2(Zr, Ce)2O7 ceramics were designed and fabricated. The influences of various Sm/Ce doping contents on the order-disorder structure of the samples were investigated systematically by XRD and Raman analysis. The microstructure, elemental composition and distribution of the samples were analyzed by SEM-EDX approach. The aqueous durability of the specimens was also evaluated by a static leaching experiment. The results showed that the Gd/Zr-sites of Gd2Zr2O7 pyrochlore could be concurrently substituted by various contents of Sm/Ce. The phase structure of the as-prepared (Gd, Sm)2(Zr, Ce)2O7 ceramics were transformed from the ordered pyrochlore phase to the disordered defect-fluorite phase with decreasing the average r[(Gd, Sm)3+]/r[(Zr, Ce)4+] radius ratio after substitution. And the ceramics fabricated in this study presented high densification and excellent aqueous durability.

In order to ascertain the structural relationship of zirconolite and pyrochlore for their potential application in HLW immobilization, the Gd-doped zirconolite-pyrochlore composite ceramics (Ca 1- x Zr 1- x Gd 2 x Ti 2 O 7 ) were systematically synthesized with x = 0.0–1.0 by traditional solid-phase reaction method. The phase evolution and microstructure of the as-prepared samples have been elucidated by XRD and Rietveld refinement, Raman spectroscopy, BSE-EDS and HRTEM analysis. The results showed that zirconolite-2M, zirconolite-4M, perovskite and pyrochlore, four phases were identified in Ca 1- x Zr 1- x Gd 2 x Ti 2 O 7 system and could be coexisted at x = 0.4 composition. With the increase of Gd 3+ substitution, the phase evolution was followed by zirconolite-2M→zirconolite-4M→pyrochlore. It is illustrated that the phase transformation from zirconolite-2M to zirconolite-4M was promoted by the preferential substitution of Gd 3+ for Ca 2+ . And the solubility of Gd 3+ in zirconolite-2M, zirconolite-4M and pyrochlore increased in sequence. The chemical stability test was also measured by the PCT leaching method. The normalized elemental release rates of Ca, Zr, Ti and Gd in Ca 1- x Zr 1- x Gd 2 x Ti 2 O 7 system were fairly low and in the range of 10 −6 −10 −8 g m −2 d −1 , which indicated a potential ceramics composite ensemble of CaZrTi 2 O 7 -Gd 2 Ti 2 O 7 system for nuclear HLW immobilization.