Structures and Stabilities of Trivalent and Tetravalent Rare Earth Ions in Sevenfold Andeightfold Coordination in Fluorite-Related Complex Oxides

Morss, Lester R.

doi:10.1557/proc-257-275

Cited by 6 publications

(1 citation statement)

References 10 publications

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“…As a part of demonstrating the utility of plutonium immobilization in these ceramics, Yamazaki et al showed that the substitution of Pu 3+ on the A sites of the zirconate-type pyrochlore (La 1– x Pu x ) 2 Zr 2 O 7+ y ( x = 0–1) was possible, but the measured solubility limit was 10 mol %, which is well within the incorporation range needed for a viable waste form because loads above ∼5% lead to the potential risk of criticality in a repository . However, recent studies have shown contrasting results that yielded the possibility that plutonium might be incorporating onto both A and B sites because of partial oxidation of Pu 3+ to Pu 4+ , − depending on whether oxidizing or reducing conditions are employed during materials preparation. − Typically the goal is to avoid multiple site substitutions, because in many cases it is the resilience of the transition-metal oxide network that is providing stability with respect to radiolytic and environmental degradation.…”

Section: Introductionmentioning

confidence: 99%

Tailored Perovskite Waste Forms for Plutonium Trapping

et al. 2019

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Perovskite ceramics have been extensively studied as host matrixes for radionuclide entrapment for nuclear waste disposal. As an expansion of these investigations, cerium, neodymium, and plutonium were incorporated into a perovskite phase, ACu 3 FeTi 3 O 12 (A = Nd, Ce, Pu), using sol−gel methods under oxidizing and reducing atmospheres. The targeted materials contained varying levels of Ce 3+ and Nd 3+ on the A site, yielding potential compositions of Nd 1−x Ce x Cu 3 FeTi 3 O 12 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.8). However, interrogation of these materials shows that the maximum Ce 3+ loading is achieved near x ≈ 0.2. A single composition with plutonium was targeted, Nd 0.9 Pu 0.1 Cu 3 FeTi 3 O 12 , in order to properly model more realistic loading levels for a repositorydestined material. These compounds were characterized using powder X-ray diffraction with Rietveld refinements of the structures and by a variety of spectroscopic techniques. The data suggest that, in order to achieve Pu 3+ substitution onto the A sites in the Nd 0.9 Pu 0.1 Cu 3 FeTi 3 O 12 , a reducing atmosphere must be employed. Otherwise, the redox activity of plutonium results in substitution onto multiple sites in the material as well as the formation of secondary phases such as TiO 2 .

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