Nano is everywhere but actinides are the forgotten elements of the nanoworld! Isotropic faceted uranium oxide nanodots and anisotropic thorium oxide nanorods were synthesized. These nano‐objects are very well crystallized and monodisperse. The characteristics of the actinide oxide nanocrystals can be controlled by tuning the reactivity of the starting actinide precursors. Such results pave the way for the synthesis of transuranium‐based nano‐objects.

Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well-defined actinide-based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non-aqueous surfactant-assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra-small diameters of 1 nm) of thorium oxide were synthesised.

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High-resolution transmission electron microscopy and electron-energy loss spectroscopy have been used to characterize the structure and chemical composition of niobium carbonitrides in the ferrite of a Fe-Nb-C-N model alloy at different precipitation stages. Experiments seem to indicate the coexistence of two types of precipitates: pure niobium nitrides and mixed substoichiometric niobium carbonitrides. In order to understand the chemical composition of these precipitates, a thermodynamic formalism has been developed to evaluate the nucleation and growth rates (classical nucleation theory) and the chemical composition of nuclei and existing precipitates. A model based on the numerical solution of thermodynamic and kinetic equations is used to compute the evolution of the precipitate size distribution at a given temperature. The predicted compositions are in very good agreement with experimental results.

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In this communication, we report on the use of easily accessible actinide precursors to synthesize actinide oxide nanocrystals. Uranyl and neptunyl nitrates have been successfully used as starting materials in the non-aqueous synthesis of AnO 2 (An = U, Np) nanocrystals. This communication reports for the first time on the formation of transuranium-based nanocrystals.The past two decades have witnessed the emergence of nanoscience and nanotechnology. 1,2 This unprecedented development is related to the fact that nano-objects exhibit size and shape dependent properties and hence can be used as new building blocks to design nanomaterials with innovative functionalities. [3][4][5] Whereas transition metal and main-group based nano-objects are extensively studied for their magnetic, optical or catalytic properties, 6-9 our knowledge is still considerably limited when dealing with actinide elements.The synthesis of actinide-based nano-objects offers a unique opportunity to study size and shape effects on the properties of 5f electrons and is of interest both for fundamental and applied research. 10,11 Whereas several groups developed the synthesis of actinide containing molecular clusters that have dimensions extending into the nanoscale, [12][13][14][15][16][17] less is known about actinidebased nanocrystals (NCs). Although thorium and uranium oxide NCs have been synthesized under various experimental conditions, [18][19][20][21][22][23][24] transuranium-based NCs have never been reported. As a consequence, versatile synthetic methods enabling the controlled synthesis (i.e. size, shape and composition) of various actinidebased NCs, and particularly transuranium-based NCs, are highly desirable.This communication reports on the use of actinyl nitrates, which are one of the most easily accessible compounds for actinides, as starting precursors in the controlled synthesis of

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