On structure and phase transformation of uranium doped La2Hf2O7 nanoparticles as an efficient nuclear waste host. (12th July 2018)

• Record Type: Journal Article
• Authors: Abdou, Maya; Gupta, Santosh K.; Zuniga, Jose P.; Mao, Yuanbing
• Is Part Of: Materials chemistry frontiers. Volume 2:Number 12(2018)
• Page Start: 2201
• Page End: 2211
• Publication Date: 2018-07-12
• Subjects: Materials science -- Periodicals; Chemistry -- Periodicals; 540
• DOI: 10.1039/c8qm00266e
• Languages: English
• ISSNs: 2052-1529

Abstract

Abstract : Doping induced phase transformation and speciation of the uranium ions in La2 Hf2 O7 nanoparticles as nuclear waste host were investigated. Abstract : 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 La2 Hf2 O7 nanoparticles (NPs) doped with uranium at different concentrations (0–10%) and investigated their structural transition. We have discovered that in our La2 Hf2 O7 :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 UO6 6− form. We also confirmed that the U 4+ ions substituted the Hf 4+ ions with a lifetime of ∼1.0 μs and the UO6 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 La2 Hf2 O7 :U NPs was higher than that of the UO6 6− ions at low doping level, but at the doping level higher than 2.5%, the fraction of the UO6 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 La2 Hf2 O7 :U NPs with increasing uranium doping level, and found that ordered pyrochlore phase favors the U 4+ ions whereas disordered cotunnite phase favors the UO6 6− ions. We further used in situ Raman spectroscopy to confirm the reversible cotunnite to pyrochlore phase transformation of the La2 Hf2 O7 :10%U NPs at 900 °C. Therefore, this work demonstrated the successful development of uranium doped La2 Hf2 O7 NPs and thorough characterization of the fundamental spectra of uranium ions, doping induced phase transformation, and structure–optical property correlation.