Effect of Oxide Ion Distribution on a Uranium Structure in Highly U-Doped RE₂Hf₂O₇ (RE = La and Gd) Nanoparticles

Abstract

Rare-earth based A 2 B 2 O 7 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, La 2 Hf 2 O 7 (LHO) and Gd 2 Hf 2 O 7 (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 6+ 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 REbased hafnates for nuclear waste hosts, sensors, thermal barrier coatings, and scintillator applications.

Highly Selective Extraction of U(VI) from Solutions by Metal Organic Framework-Based Nanomaterials through Sorption, Photochemistry, and Electrochemistry Strategies

“…The rapid development of the economy and industry is increasing the amount of energy demands. − The energy crisis has become a whole world problem because large amounts of CO 2 and other wastes are produced in the generation of electricity. , Nuclear energy has attracted worldwide attention in power energy supply, which not only is attributed to its low CO 2 emission but also is attributed to the high energy output in the nuclear fission process. − However, the rapid development of nuclear energy requires a sustainable supply of nuclear fuel. , The release of uranium to the natural environment in the mining process not only generates large amounts of U-containing wastewater but also results in environmental pollution and human health dangers. − Thereby, achieving the goal of efficiently and selectively removing U­(VI) from complex systems is important not only for environmental pollution management but also for nuclear fuel supply and cycles.…”

Metal–Organic Framework-Based Materials for Adsorption and Detection of Uranium(VI) from Aqueous Solution

“…Therefore, the development of convenient, effective, and on-site uranyl adsorbents, sensors, and adsorptive sensors have received more and more attention. Along with several other groups, we have recently focused our research on the adsorption, immobilization, and detection of uranium simultaneously. − …”

Controllable sites and high-capacity immobilization of uranium in Nd2Zr2O7 pyrochlore

“…Principally, molten salt synthesis is a potential methodology that can lower the reaction temperature due to faster mass transport. In previous work (Mao et al, 2009;Gupta & Mao, 2021), La 2 Zr 2 O 7 pyrochlore ceramic was synthesized via the molten salt method by heating mixtures at 650 C for 6 h. However, until now, only limited work has been reported on actinide-incorporated pyrochlore via the molten salt method (Abdou et al, 2018(Abdou et al, , 2019Wang et al, 2020). Neodymium zirconate has also been proposed as a potential ceramic matrix for the immobilization of nuclear waste; therefore, in this work, we chose Nd 2 Zr 2 O 7 as a suitable host material for studying uranium immobilization via a molten salt process.…”