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Title: On structure and phase transformation of uranium doped La 2 Hf 2 O 7 nanoparticles as an efficient nuclear waste host
The design and development of efficient and stable nuclear waste hosts has drawn intensive interest for long-lived lanthanides and actinides. A detailed investigation of their structure and potential structural evolution are crucial. In this study, we have synthesized lanthanum hafnate La 2 Hf 2 O 7 nanoparticles (NPs) doped with uranium at different concentrations (0–10%) and investigated their structural transition. We have discovered that in our La 2 Hf 2 O 7 :U NPs, the uranium dopants are stabilized at both U 4+ and U 6+ oxidation states in which the U 6+ oxidation state exists in octahedral uranate UO 6 6− form. We also confirmed that the U 4+ ions substituted the Hf 4+ ions with a lifetime of ∼1.0 μs and the UO 6 6− ions resided at the La 3+ sites with a lifetime of ∼9.0 μs. More interestingly, the proportion of the U 4+ ions in the La 2 Hf 2 O 7 :U NPs was higher than that of the UO 6 6− ions at low doping level, but at the doping level higher than 2.5%, the fraction of the UO 6 6− ions was greater than that of the U 4+ ions. Furthermore, we studied the structural phase transformation from order pyrochlore to cotunnite of these La 2 Hf 2 O 7 :U NPs with increasing uranium doping level, and found that ordered pyrochlore phase favors the U 4+ ions whereas disordered cotunnite phase favors the UO 6 6− ions. We further used in situ Raman spectroscopy to confirm the reversible cotunnite to pyrochlore phase transformation of the La 2 Hf 2 O 7 :10%U NPs at 900 °C. Therefore, this work demonstrated the successful development of uranium doped La 2 Hf 2 O 7 NPs and thorough characterization of the fundamental spectra of uranium ions, doping induced phase transformation, and structure–optical property correlation.  more » « less
Award ID(s):
1710160
NSF-PAR ID:
10098129
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Materials Chemistry Frontiers
Volume:
2
Issue:
12
ISSN:
2052-1537
Page Range / eLocation ID:
2201 to 2211
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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