On structure and phase transformation of uranium doped La2Hf2O7 nanoparticles as an efficient nuclear waste host,Materials Chemistry Frontiers

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On structure and phase transformation of uranium doped La2Hf2O7 nanoparticles as an efficient nuclear waste host
Materials Chemistry Frontiers ( IF 6.0 ) Pub Date : 2018-06-26 , DOI: 10.1039/c8qm00266e
Maya Abdou _{1,

2,

3,

4} , Santosh K. Gupta _{1,

2,

3,

4,

5} , Jose P. Zuniga _{1,

2,

3,

4} , Yuanbing Mao _{1,

2,

3,

4,

6}

Affiliation

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 La₂Hf₂O₇ nanoparticles (NPs) doped with uranium at different concentrations (0–10%) and investigated their structural transition. We have discovered that in our La₂Hf₂O₇:U NPs, the uranium dopants are stabilized at both U⁴⁺ and U⁶⁺ oxidation states in which the U⁶⁺ oxidation state exists in octahedral uranate UO₆⁶⁻ form. We also confirmed that the U⁴⁺ ions substituted the Hf⁴⁺ ions with a lifetime of ∼1.0 μs and the UO₆⁶⁻ ions resided at the La³⁺ sites with a lifetime of ∼9.0 μs. More interestingly, the proportion of the U⁴⁺ ions in the La₂Hf₂O₇:U NPs was higher than that of the UO₆⁶⁻ ions at low doping level, but at the doping level higher than 2.5%, the fraction of the UO₆⁶⁻ ions was greater than that of the U⁴⁺ ions. Furthermore, we studied the structural phase transformation from order pyrochlore to cotunnite of these La₂Hf₂O₇:U NPs with increasing uranium doping level, and found that ordered pyrochlore phase favors the U⁴⁺ ions whereas disordered cotunnite phase favors the UO₆⁶⁻ ions. We further used in situ Raman spectroscopy to confirm the reversible cotunnite to pyrochlore phase transformation of the La₂Hf₂O₇:10%U NPs at 900 °C. Therefore, this work demonstrated the successful development of uranium doped La₂Hf₂O₇ NPs and thorough characterization of the fundamental spectra of uranium ions, doping induced phase transformation, and structure–optical property correlation.

中文翻译：

铀掺杂La ₂ Hf ₂ O ₇纳米粒子作为高效核废料主体的结构和相变研究

高效稳定核废料宿主的设计和开发引起了人们对长寿命镧系元素和act系元素的浓厚兴趣。对它们的结构和潜在的结构演变进行详细研究至关重要。在这项研究中，我们合成了掺杂有不同浓度（0-10％）铀的重晶镧镧La ₂ Hf ₂ O ₇纳米颗粒（NPs），并研究了它们的结构转变。我们已经发现，在我们的La ₂ Hf ₂ O ₇：U NP中，铀掺杂剂稳定在U ⁴⁺和U ⁶⁺氧化态下，其中U ⁶⁺氧化态存在于八面体尿酸盐UO中。₆⁶⁻形式。我们还证实，U⁴⁺离子取代Hf⁴⁺离子的寿命约为1.0μs，UO₆^6-离子位于La³⁺位点的寿命约为9.0μs。更有趣的是，在低掺杂水平下，La₂ Hf₂ O₇：U NPs中U⁴⁺离子的比例高于UO₆^6-离子中的比例，但是在高于2.5％的掺杂水平下，的UO₆⁶⁻离子大于U^4+的离子离子。此外，我们研究了随着铀掺杂水平的提高，这些La ₂ Hf ₂ O ₇：U NP从有序烧绿石向共co石的结构相变，发现有序的烧绿石相有利于U ⁴⁺离子，而无序的tun石相有利于UO _6。^6-离子。我们进一步使用原位拉曼光谱法确定了900°C时La ₂ Hf ₂ O ₇：10％U NPs的可逆方铁矿到烧绿石相变。因此，这项工作证明了铀掺杂La ₂ Hf ₂ O ₇的成功开发。纳米粒子和铀离子基本光谱的彻底表征，掺杂引起的相变以及结构-光学性质的相关性。

更新日期：2018-11-24

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