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Etude nano-structurale de superréseaux d'oxydes ferroélectriques

Abstract : The aim of this work was to go deeply into the nanostructural description of ferroelectric thin films and interfaces. For this purpose we used synchrotron radiation based techniques to study various superlattices. Texture studies show the very good epitaxy of superlattices (BaTiO3/SrTiO3)n. Along the growth axis, we observe a modulation of the lattice on a large scale. However, generally, the film is coherent (from X-ray diffraction point of view) on only 30 % of its thickness. Moreover, Sr and Ba diffuse significantly at the interfaces. The maps in asymmetric diffraction mode show the in-plane difference between the lattice parameters of the multilayer and the substrate, whereas the in-plane lattice parameters of the layers SrTiO3 and BaTiO3 are almost equal. The Transmission Electron Microscopy shows the need to take into account the asymmetry of both the structural and the chemical profiles in each layer. These images show the evolution of the structural quality of these superlattices, from the interface with the substrate to the free surface of the superlattice. For the (PbTiO3/BaTiO3)n superlattices, we report that the strain is partially relaxed for thick films. The chemical interdiffusion of lead and barium is very lower compared to the one of the Sr/Ba system. The PbTiO3 sublayer exhibits a preferential orientation of the domains, with a polar axis contained in the growth plane. For the (La0,7Sr0,3MnO3/SrTiO3)n superlattices, the reflectivity shows not much chemical diffusion and roughness at the interfaces. X-ray diffraction shows the high structural quality of the interfaces (with fringes between Bragg peaks). The simulation points out an excellent coherence of the superlattice and abrupt interfaces.
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https://tel.archives-ouvertes.fr/tel-00007653
Contributor : Maud Nemoz <>
Submitted on : Monday, December 6, 2004 - 5:26:26 PM
Last modification on : Friday, December 18, 2020 - 1:34:02 PM
Long-term archiving on: : Thursday, September 13, 2012 - 1:25:26 PM

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  • HAL Id : tel-00007653, version 1

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Maud Nemoz. Etude nano-structurale de superréseaux d'oxydes ferroélectriques. Matériaux. Université Joseph-Fourier - Grenoble I, 2004. Français. ⟨tel-00007653⟩

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