Open AccessControllable sites and high‐capacity immobilization of uranium in Nd 2 Zr 2 O 7 pyrochlore
Author(s) -
Sun Jian,
Zhou Jing,
Hu Zhiwei,
Chan Ting-Shan,
Liu Renduo,
Yu Haisheng,
Zhang Linjuan,
Wang Jian-Qiang
Publication year - 2022
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s1600577521012558
Subject(s) - pyrochlore , uranium , x ray absorption fine structure , uranyl , materials science , thorium , actinide , fluorite , raman spectroscopy , analytical chemistry (journal) , phase (matter) , crystallography , inorganic chemistry , chemistry , spectroscopy , metallurgy , quantum mechanics , optics , physics , organic chemistry , chromatography
As potential nuclear waste host matrices, two series of uranium‐doped Nd 2 Zr 2 O 7 nanoparticles were successfully synthesized using an optimized molten salt method in an air atmosphere. Our combined X‐ray diffraction, Raman and X‐ray absorption fine‐structure (XAFS) spectroscopy studies reveal that uranium ions can precisely substitute the Nd site to form an Nd 2– x U x Zr 2 O 7+δ (0 ≤ x ≤ 0.2) system and the Zr site to form an Nd 2 Zr 2– y U y O 7+δ (0 ≤ y ≤ 0.4) system without any impurity phase. With increasing U concentration, there is a phase transition from pyrochlore ( Fd 3 m ) to defect fluorite ( Fm 3 m ) structures in both series of U‐doped Nd 2 Zr 2 O 7 . The XAFS analysis indicates that uranium exists in the form of high‐valent U 6+ in all samples. To balance the extra charge for substituting Nd 3+ or Zr 4+ by U 6+ , additional oxygen is introduced accompanied by a large structural distortion; however, the Nd 2 Zr 1.6 U 0.4 O 7+δ sample with high U loading (20 mol%) still maintains a regular fluorite structure, indicating the good solubility of the Nd 2 Zr 2 O 7 host for uranium. This study is, to the best of our knowledge, the first systematic study on U‐incorporated Nd 2 Zr 2 O 7 synthesized via the molten salt method and provides convincing evidence for the feasibility of accurately immobilizing U at specific sites.