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Fluorite-derived high-entropy ceramic waste form for immobilizing multi-nuclides with multi-valence: a case study of Nb5+ as charge compensator.

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Title: Fluorite-derived high-entropy ceramic waste form for immobilizing multi-nuclides with multi-valence: a case study of Nb5+ as charge compensator.
Authors: Ji, Xiuhua1,2,3 (AUTHOR), Wang, Lielin1,2 (AUTHOR) wanglielin@swust.edu.cn, Ji, Shiyin1,2 (AUTHOR) jishy@swust.edu.cn, Zhang, Sinian3 (AUTHOR), Fang, Shuohai3 (AUTHOR), Xu, Jiaqi3 (AUTHOR), Shih, Kaimin4 (AUTHOR), Liao, Changzhong1,3 (AUTHOR) liaocz29@connect.hku.hk
Source: Ceramics International. May2026:Part A, Vol. 52 Issue 11, p15399-15407. 9p.
Subjects: Pyrochlore, Radioactive waste sites, Ceramics, Radioisotopes, Oxide ceramics
Abstract: Given its significant radiological hazards to public safety, high-level radioactive waste (HLW) must be immobilized into stable waste forms for long-term geological disposal. High-entropy ceramics have garnered significant research interest for their unique ability to simultaneously immobilize multiple radionuclides. In this work, aiming to immobilize multivalent actinides (simulated by REEs) using Nb as charge compensator, a series of novel high-entropy zirconolite samples were successfully synthesized via high temperature solid-state reaction. The compositions were designed as CaZr 1-5x REE 5x Ti 2-5x Nb 5x O 7 (REE = Nd, Sm, Gd, Ho, Yb; x = 0.02, 0.05, 0.10, 0.15, 0.20) and CaZr 1-6x Ce x REE 5x Ti 2-5x Nb 5x O 7 (REE = Nd, Sm, Gd, Ho, Yb; x = 0.02, 0.04, 0.08, 0.10, 0.15). The powder XRD, back-scattered SEM and Raman characterization results revealed a phase evolution following the zirconolite-2M→zirconolite-4M→pyrochlore pathway in those two-type compositions. For CaZr 1-5x REE 5x Ti 2-5x Nb 5x O 7 type high-entropy ceramics, a small amount of perovskite was observed alongside zirconolite. A single-phase pyrochlore structure was obtained at x ≥ 0.10. For compositions with CaZr 1-6x Ce x REE 5x Ti 2-5x Nb 5x O 7 , trace perovskite phase was detected throughout the solid-solution range, which may be attributed to the fluctuations of Ce oxidation state. Interestingly, the Raman spectra displayed signification difference in difference excitation wavelength. The reasons should be attributed to the resonant enhancement or suppression of specific modes due to elemental doping and the contribution from background fluorescence. This study revealed that the structural adaptability of fluorite-derived high-entropy ceramics makes them well-suited for the immobilization of high-level waste, particularly for actinides. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Given its significant radiological hazards to public safety, high-level radioactive waste (HLW) must be immobilized into stable waste forms for long-term geological disposal. High-entropy ceramics have garnered significant research interest for their unique ability to simultaneously immobilize multiple radionuclides. In this work, aiming to immobilize multivalent actinides (simulated by REEs) using Nb as charge compensator, a series of novel high-entropy zirconolite samples were successfully synthesized via high temperature solid-state reaction. The compositions were designed as CaZr 1-5x REE 5x Ti 2-5x Nb 5x O 7 (REE = Nd, Sm, Gd, Ho, Yb; x = 0.02, 0.05, 0.10, 0.15, 0.20) and CaZr 1-6x Ce x REE 5x Ti 2-5x Nb 5x O 7 (REE = Nd, Sm, Gd, Ho, Yb; x = 0.02, 0.04, 0.08, 0.10, 0.15). The powder XRD, back-scattered SEM and Raman characterization results revealed a phase evolution following the zirconolite-2M→zirconolite-4M→pyrochlore pathway in those two-type compositions. For CaZr 1-5x REE 5x Ti 2-5x Nb 5x O 7 type high-entropy ceramics, a small amount of perovskite was observed alongside zirconolite. A single-phase pyrochlore structure was obtained at x ≥ 0.10. For compositions with CaZr 1-6x Ce x REE 5x Ti 2-5x Nb 5x O 7 , trace perovskite phase was detected throughout the solid-solution range, which may be attributed to the fluctuations of Ce oxidation state. Interestingly, the Raman spectra displayed signification difference in difference excitation wavelength. The reasons should be attributed to the resonant enhancement or suppression of specific modes due to elemental doping and the contribution from background fluorescence. This study revealed that the structural adaptability of fluorite-derived high-entropy ceramics makes them well-suited for the immobilization of high-level waste, particularly for actinides. [ABSTRACT FROM AUTHOR]
ISSN:02728842
DOI:10.1016/j.ceramint.2026.02.145