Modelling bulk and surface characteristics of cubic CeO2, Gd2O3, and gadolinium-doped ceria using a partial charge framework

The development and characterization of materials for solid oxide fuel cells (SOFC) is an important step towards sustainable energy technologies. This present study models cubic CeO2, Gd2O3, and gadolinium-doped ceria (GDC) using newly constructed interaction potentials based on a partial atom charge framework. The interaction model was validated by comparing the structural properties with experimental reference data, which were found to be in good agreement. Validation of the potential model was conducted considering the surface stability of CeO2 and Gd2O3. Additionally, the accuracy of the novel potential model was assessed by comparing the oxygen diffusion coefficient in GDCn (n = 4-15) and the associated activation energy. The results demonstrate that the novel potential model is capable of describing the oxygen diffusion in GDC. In addition, this study compares the vibrational properties of the bulk with density functional theory (DFT) calculations, using a harmonic frequency analysis that avoids the need for computationally expensive quantum mechanical molecular dynamics (QM MD) simulations. The potential is compatible with a reactive water model, thus providing a framework for the simulation of solid-liquid interfaces.

Morphological and functional effects of graphene on the synthesis of uranium carbide for isotopes production targets

The development of tailored targets for the production of radioactive isotopes represents an active field in nuclear research. Radioactive beams find applications in nuclear medicine, in astrophysics, matter physics and materials science. In this work, we study the use of graphene both as carbon source for UO₂ carbothermal reduction to produce UC_x targets, and also as functional properties booster. At fixed composition, the UC_x target grain size, porosity and thermal conductivity represent the three main points that affect the target production efficiency. UC_x was synthesized using both graphite and graphene as the source of carbon and the target properties in terms of composition, grain size, porosity, thermal diffusivity and thermal conductivity were studied. The main output of this work is related to the remarkable enhancement achieved in thermal conductivity, which can profitably improve thermal dissipation during operational stages of UC_x targets.

Aliovalent Cation Substitution in UO2: Electronic and Local Structures of U1-yLayO2±x Solid Solutions

For nuclear fuel related applications, the oxygen stoichiometry of mixed oxides U_1-yM_yO_2±x is an essential property as it affects fuel properties and may endanger the safe operation of nuclear reactors. A careful review of the open literature indicates that this parameter is difficult to assess properly and that the nature of the defects, i.e., oxygen vacancies or U^V, in aliovalent cation-doped UO₂ is still subject to controversy. To confirm the formation of U^V, we have investigated the room-temperature stable U_1-yLa_yO_2±x phase using several experimental methods (e.g., XRD, XANES, and NMR) confirmed by theoretical calculations. This paper presents the experimental proof of U^V and its effect we identified in both electronic and local structure. We observe that U^V is formed in quasi-equimolar proportion as La^III in U_1-yLa_yO_2±x (y = 0.06, 0.11, and 0.22) solid solutions. The fluorite structure is maintained despite the cationic substitution, but the local structure is affected as variations of the interatomic distances are found. Therefore, we provide here the definitive proof that the substitution of U^IV with La^III is not accommodated by the creation of O vacancies as has often been assumed. The UO₂ fluorite structure compensates the incorporation of an aliovalent cation by the formation of U^V in quasi-equimolar proportions.

A low-temperature synthesis method for AnO2 nanocrystals (An = Th, U, Np, and Pu) and associate solid solutions

Actinide oxalate decomposition under hot compressed water is proposed as a milder production route for nanometric sized (mixed) actinide oxides.