Wang Yuming, Darapaneni Pragathi, Ofoegbuna Tochukwu, Gupta Santosh K, Kizilkaya Orhan, Mao Yuanbing, Dorman James A
Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
Inorg Chem. 2020 Oct 5;59(19):14070-14077. doi: 10.1021/acs.inorgchem.0c01850. Epub 2020 Sep 22.
Rare-earth based ABO compounds have been considered as potential host materials for nuclear waste due to their exceptional chemical, physical, capability of accommodating high concentration of actinides at both A- and B-sites, negligible leaching, tendency to form antisite defects, and radiation stabilities. In this work, LaHfO (LHO) and GdHfO (GHO) nanoparticles (NPs) were chosen as the RE-based hafnates to study the structural changes and the formation of different U molecular structures upon doping (or alloying) at high concentration (up to 30 mol %) using a combined coprecipitation and molten-salt synthesis. These compounds form similar crystal structures, i.e., ordered pyrochlore (LHO) and disordered fluorite (GHO), but are expected to show different phase transformations at high U doping concentration. X-ray diffraction (XRD) and Rietveld refinement results show that the LHO:U NPs have high structural stability, whereas the GHO:U NPs exhibit a highly disordered structure at high U concentration. Alternatively, the vibrational spectra show an increasingly random oxygen distribution with U doping, driving the LHO:U NPs to the disordered fluorite phase. X-ray spectroscopy indicates that U is stabilized as different U species in both LHO and GHO hosts, resulting in the formation of oxygen vacancies stemming from the U local coordination and different phase transformation. Interestingly, the disordered fluorite phase has been reported to have increased radiation tolerance, suggesting multiple benefits associated with the LHO host. These results demonstrate the importance of the structural and chemical effect of actinide dopants on similar host matrices which are important for the development of RE-based hafnates for nuclear waste hosts, sensors, thermal barrier coatings, and scintillator applications.
基于稀土的ABO化合物因其特殊的化学、物理性质，在A位和B位都能容纳高浓度锕系元素的能力、可忽略不计的浸出率、形成反位缺陷的倾向以及辐射稳定性，而被视为核废料的潜在主体材料。在这项工作中，选择了LaHfO（LHO）和GdHfO（GHO）纳米颗粒（NPs）作为基于稀土的铪酸盐，以研究在高浓度（高达30摩尔%）掺杂（或合金化）时的结构变化以及不同U分子结构的形成，采用共沉淀和熔盐合成相结合的方法。这些化合物形成相似的晶体结构，即有序的烧绿石（LHO）和无序的萤石（GHO），但预计在高U掺杂浓度下会表现出不同的相变。X射线衍射（XRD）和Rietveld精修结果表明，LHO:U NPs具有高结构稳定性，而GHO:U NPs在高U浓度下表现出高度无序的结构。另外，振动光谱显示随着U掺杂，氧分布越来越随机，促使LHO:U NPs转变为无序的萤石相。X射线光谱表明，U在LHO和GHO主体中均以不同的U物种形式稳定存在，导致由于U的局部配位和不同的相变而形成氧空位。有趣的是，据报道无序萤石相具有更高的辐射耐受性，这表明LHO主体具有多种益处。这些结果证明了锕系元素掺杂剂对相似主体基质的结构和化学效应的重要性，这对于开发用于核废料主体、传感器、热障涂层和闪烁体应用的基于稀土的铪酸盐至关重要。
