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Etude à l'échelle atomique de la plasticité et de la sur-stœchiométrie dans le dioxyde d'uranium

Abstract : The aim of this work is to study on the first hand plasticity in uranium dioxide by the mean of an atomic scale characterization of dislocations glide mechanisms, and on the other hand to study hyper-stoichiometric uranium dioxide by the determination of atomic configurations and their relations that appear on the phase diagram as a function of O/U ratio and temperature. To achieve this, we perform atomic scale simulations by energy minimization and molecular dynamics using a complex variable charge empirical potential, which let the ionic charges vary as the local atomic environment is modified. We firstly characterize plasticity in UO₂ single crystals and show that it is governed in the {100} main glide planes by thermally activated edge dislocations glide at low temperatures by a mechanism of nucleation and growth of kink pairs on these dislocations. Then, the same empirical potential let us derive at the atomic scale the structure of the high temperature disordered UO₂₊ₓ phase and the evolution with temperature of the ordered structure U₄O₉. This gives an atomistic description of part of the U-O phase diagram. So, the tool we use, a variable charge empirical potential, let us understand more precisely UO₂ properties, and more generally we prove that this kind of tool is a promising alternative to classical empirical potentials and ab-initio methods to model complex atomic systems.
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Submitted on : Friday, December 7, 2018 - 2:47:08 PM
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  • HAL Id : tel-01948217, version 1

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Aurélien Soulié. Etude à l'échelle atomique de la plasticité et de la sur-stœchiométrie dans le dioxyde d'uranium. Science des matériaux [cond-mat.mtrl-sci]. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLS353⟩. ⟨tel-01948217⟩

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