Synthesis, characterization and thermal expansion measurements on uranium–cerium mixed oxides

Charge Distribution in U1–xCexO2+y Nanoparticles

“…Contrary to other substituted-UO 2 compounds, 11−13 no charge-transfer reaction between U IV and Ce IV leading to the formation Ce III and U V has been reported. Indeed, when the mixed oxides are prepared in the right oxygen potential condition to obtain stoichiometric compound U 1−x Ce x O 2.00 , their lattice parameters closely follow Vegard's law, 8,14 suggesting the progressive substitution of U IV by the Ce IV cation as a function of the composition. Even though there have been several investigations on the redox behavior of Ce-doped UO 2 mainly on thin films using extreme surface-sensitive techniques, 6,7,15 there is none for NP materials.…”

“…Due to their structural similarity, uranium and cerium dioxide form a solid solution covering the full compositional range of the Ce content. − Several articles have been published on the U 1– x Ce x O 2+ y properties (electrical conductivity, magnetic properties, oxygen potential, lattice parameter, heat capacity, thermal expansion, and phase diagram). ,− Some interesting results have also been reported on both U and Ce valences. Contrary to other substituted-UO 2 compounds, − no charge-transfer reaction between U IV and Ce IV leading to the formation Ce III and U V has been reported.…”

Fabrication of Nd- and Ce-doped uranium dioxide microspheres via internal gelation

“…The experimental lattice parameters of this study for Ce dopant contents below the solubility limit of 22.4 mol% agree well to reference data [ 37] (figure 10). The reference material was prepared by solid-state synthesis and co-precipitation [35], but also a citrate combustion method [36,37] was applied. The obtained powders were pelletised and sintered in Ar/H 2 mixtures with H 2 contents of 5 % or 8 %, equilibrated with water (O 2 potential: −416 kJ mol −1 to −347 kJ mol −1 ), the sintering temperatures ranged between 800 • C and 1450 • C. Even though a remarkably lower sintering temperature was applied, Venkata Krishnan et al [36] and Sali et al [37] obtained single phase solid solutions for compositions with Ce contents > 22.4 mol%, following the trend we observed for the majority phase in our samples.…”

“…Figure10: Lattice parameter a as function of the Ce molar metal fraction of the sintered, Ce-doped microspheres, compared to literature data[35][36][37]. The uncertainties are given with a confidence level of 2σ.…”

Influence of Sintering Conditions on the Structure and Redox Speciation of Homogeneous (U,Ce)O2+δ Ceramics: A Synchrotron Study

“…Even if they do not constitute perfect surrogates, for example, due to differences in the U–Ce–O and U–Pu–O ternary phase diagrams, cerium still possesses similar stable oxidation states to plutonium in oxide compounds as well as a close ionic radius in the eightfold coordination (0.97 Å for Ce­(IV) vs 0.96 Å for Pu­(IV)) . Hence, some efforts have been made both to prepare uranium–cerium dioxide samples with different morphologies (including nanopowders, thin films, or dense pellets) − and, in some cases, to investigate their behavior during dissolution tests . In such studies, several biases can be pointed out and preclude a reliable determination of the sample oxygen stoichiometry expressed through the O/M ratio with M = U + Ce.…”