Synthesis, Characterization, and Stability of Two Americium Vanadates, AmVO and AmVO.

In search for chemically stable americium compounds with high power densities for radioisotope sources for space applications, AmVO and AmVO were prepared by a solid-state reaction. We present here their crystal structure at room temperature solved by powder X-ray diffraction combined with Rietveld refinement. Their thermal and self-irradiation stabilities have been studied.

New insights into the structural transition from UO to UO by quantitative Raman spectroscopy.

The study of uranium oxides at different conditions is of paramount importance in the nuclear field, especially regarding characterization of the spent nuclear fuel behavior in dry storage scenarios. This paper reports results of XRD and Raman analysis on four powdered samples prepared in order to cover a specific stoichiometry range in UO, = 0.24, 0.

Synthesis and characterization of homogeneous (U,Am)O and (U,Pu,Am)O nanopowders.

This paper details the first dedicated production of homogeneous nanocrystalline particles of mixed actinide oxide solid solutions containing americium. The target compositions were UPuAmO, UAmO and UAmO. After successful hydrothermal synthesis and chemical characterisation, the nanocrystals were sintered and their structure and behaviour under self-irradiation were studied by powder XRD.

Charge Distribution in UCeO Nanoparticles.

In view of safe management of the nuclear wastes, a sound knowledge of the atomic-scale properties of UMO nanoparticles is essential. In particular, their cation valences and oxygen stoichiometries are of great interest as these properties drive their diffusion and migration behaviors into the environment. Here, we present an in-depth study of UCeO, over the full compositional domain, by combining X-ray diffraction and high-energy resolution fluorescence detection X-ray absorption near-edge structure.

Synthesis, Characterization, and Stability of Americium Phosphate, AmPO.

AmPO was prepared by a solid-state reaction method, and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. The purity of the monazite-like phase was confirmed by spectroscopic (high-resolution solid-state P NMR and Raman) and microscopic (SEM-EDX and TEM) techniques. The thermal and self-irradiation stability have been studied.

Plutonium and Americium Aluminate Perovskites.

Both AmAlO and PuAlO perovskites have been synthesized and characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). AmAlO perovskite showed a rhombohedral configuration (space group 3̅) in agreement with previous studies. The effect of americium α-decay on this material has been followed by XRD and Al MAS NMR analyses.

Optimization of Uranium-Doped Americium Oxide Synthesis for Space Application.

Americium 241 is a potential alternative to plutonium 238 as an energy source for missions into deep space or to the dark side of planetary bodies. In order to use the Am isotope for radioisotope thermoelectric generator or radioisotope heating unit (RHU) production, americium materials need to be developed. This study focuses on the stabilization of a cubic americium oxide phase using uranium as the dopant.

Aliovalent Cation Substitution in UO: Electronic and Local Structures of ULaO Solid Solutions.

For nuclear fuel related applications, the oxygen stoichiometry of mixed oxides UMO 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.

Fingerprint of local disorder in long range ordered isometric pyrochlores.

The detailed characterization of local order and disorder in isometric ABO crystalline pyrochlores is of significant importance in view of their wide range and sensitive technological applications. Nevertheless, much remains to be understood concerning their atomic scale structures. Here we specifically pinpoint local order and disorder in four stoichiometric LnZrO (Ln = La, Nd, Sm and Eu) pyrochlores using a combination of three standard easily available laboratory techniques: XRD, O solid-state MAS NMR and Raman spectroscopy.

Further insights into the chemistry of the Bi-U-O system.

Cubic fluorite-type phases have been reported in the U(IV)O2-Bi2O3 system for the entire compositional range, but an unusual non-linear variation of the lattice parameter with uranium substitution has been observed. In the current extensive investigation of the uranium(iv) oxide-bismuth(iii) oxide system, this behaviour of the lattice parameter evolution with composition has been confirmed and its origin identified. Even under inert atmosphere at 800 °C, U(IV) oxidises to U(V)/U(VI) as a function of the substitution degree.

Structural Investigation of (U0.7Pu0.3)O2-x Mixed Oxides.

Uranium-plutonium mixed oxide containing 30% of plutonium is a candidate fuel for several fast neutron and accelerator driven reactor systems. In this work, a detailed structural investigation on sol-gel synthesized stoichiometric U0.7Pu0.

High-resolution solid-state oxygen-17 NMR of actinide-bearing compounds: an insight into the 5f chemistry.

A massive interest has been generated lately by the improvement of solid-state magic-angle spinning (MAS) NMR methods for the study of a broad range of paramagnetic organic and inorganic materials. The open-shell cations at the origin of this paramagnetism can be metals, transition metals, or rare-earth elements. Actinide-bearing compounds and their 5f unpaired electrons remain elusive in this intensive research area due to their well-known high radiotoxicity.

Isolation of the large {actinide}38 poly-oxo cluster with uranium.

By controlling the water content, a new poly-oxo-metalate species containing 38 uranium centers has been solvothermally synthesized in the presence of benzoic acid in tetrahydrofuran (THF). The {U38} motif contains a distorted UO2 core of fluorite type, stabilized by benzoate and THF molecules. This compound is analogous to the {Pu38} motif and was characterized by X-ray photoelectron spectroscopy and magnetic analyses.

Three-dimensional MOF-type architectures with tetravalent uranium hexanuclear motifs (U6O8).

Four metal-organic frameworks (MOF) with tetravalent uranium have been solvothermally synthesized by treating UCl4 with rigid dicarboxylate linkers in N,N-dimethylfomamide (DMF). The use of the ditopic ligands 4,4'-biphenyldicarboxylate (1), 2,6-naphthalenedicarboxylate (2), terephthalate (3), and fumarate (4) resulted in the formation of three-dimensional networks based on the hexanuclear uranium-centered motif [U6O4(OH)4(H2O)6]. This motif corresponds to an octahedral configuration of uranium nodes and is also known for thorium in crystalline solids.

Molten salt synthesis of a mixed-valent lanthanide(III/IV) oxychloride with an unprecedented Sillen X(2)(4) structure: Ce1.3Nd0.7O3Cl.

A new cerium neodymium oxychloride, Ce1.3Nd0.7O3Cl, has been synthesized by precipitation in a LiCl–CaCl2 molten salt by humid argon sparging.

Metal-organic-framework-type 1D-channel open network of a tetravalent uranium trimesate.

An uranium trimesate open framework is built up from trinuclear building blocks (μ(3)-OU(3)) connected to each other by tricarboxylate linkers to generate honeycomb-like 3D topology. This compound was solvothermally synthesized from low-valent uranium in an N,N-dimethylformamide solvent under an inert atmosphere, favoring stabilization of the tetravalent oxidation state, which is confirmed by X-ray photoelectron spectroscopy analysis.

Planned failures from the principle of maximum site occupancy in lanthanide helicates.

Despite the recent emergence of a toolbox fitted with microscopic thermodynamic descriptors for predicting the stabilities and speciations of polynuclear complexes in solution, the discovery of novel or unusual type of metal-ligand assemblies in metallosupramolecular chemistry still often relies on serendipity. In order to highlight the novel perspectives offered by a rational exploitation of these thermodynamic parameters, the segmental bis-tridentate ligands L7 and L8 have been designed for providing effective molarities upon reaction with trivalent lanthanides, Ln(III), so small that the saturated binuclear triple-stranded helicates [Ln(2)(Lk)(3)](6+), which obey the well-respected principle of maximum site occupancy, cannot be detected in solution because of their deliberately planned instabilities. The hierarchical evolution of the effective molarities with an increasing number of ligand strands in these complexes indeed favors the formation of the alternative unsaturated single-stranded [Ln(2)(Lk)](6+) and double-stranded [Ln(2)(Lk)(2)](6+) complexes, whose relative speciations in solution depend on the nature of the binding sites introduced into the segmental ligand.