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Etude de la fléxoélectricité de nanosystèmes par le développement d'algorithmes mêlant approche atomistique et mécanique des milieux continus

Abstract : The flexoelectricity tensor of a material characterizes its ability to polarize under the action of a deformation gradient. The phenomenon is still rarely used though it exists in every material, because the effects are usually very weak. However, for nanoscale systems, flexoelectricity can be largely enhanced because of a possibly much greater gradient. Thus, the aim of this PHD thesis is to build a model that would allow us to compute the characteristic tensors of flexoelectricity in order to design a nanosytem in which huge flexoelectric effects could be used for energy conversion. For that purpose, we have studied the flexion of several semi-conducting Single-Wall Carbon NanoTubes (SWCNT), considered either as continuous cylinders or as a discrete network of carbon atoms. In the continuum point of view, we have applied the principle of virtual powers and classical thermodynamics to systematically obtain the constitutive equations of a semi-conducting, electro-magnetic deformable continuum, including the effects of the deformation, polarization and magnetization gradients. Meanwhile, we have improved an atomistic model with distributed permanent and induced dipoles to simulate the inverse flexoelectric effect on the SWCNTs. Using homogenization hypothesis, we have coupled these two approaches by obtaining the equations binding the atomistic quantities computed in the numerical simulations, with the corresponding macroscopic quantities used in the previously obtained constitutive equations. The first numerical results seem to show a notable variation of the elements of the flexoelectric tensors as a function of the radius and length of the SWCNT.
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https://tel.archives-ouvertes.fr/tel-02466846
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  • HAL Id : tel-02466846, version 1

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Gautier Lecoutre. Etude de la fléxoélectricité de nanosystèmes par le développement d'algorithmes mêlant approche atomistique et mécanique des milieux continus. Mécanique des matériaux [physics.class-ph]. Université Bourgogne Franche-Comté, 2018. Français. ⟨NNT : 2018UBFCD012⟩. ⟨tel-02466846⟩

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