Topology of ferroelectric polarization at the BaTiO3(001) surface from ab initio calculations and electron microscopy-spectroscopy

Jelle Dionot 1
1 LENSIS - Laboratoire d'Etude des NanoStructures et Imagerie de Surface
SPEC - UMR3680 - Service de physique de l'état condensé, IRAMIS - Institut Rayonnement Matière de Saclay
Abstract : At a surface or interface of a ferroelectric material, the polarization can be destabilized and even suppressed by the depolarizing field which arises from uncompensated polarization charge. In the absence of external (adsorbates, electrodes) or internal (defects, dopants) screening mechanisms, domain ordering is the most natural way for a system to remain ferroelectric and minimize its electrostatic energy. This thesis focuses on the study of the stability of various possible domain configurations, and on how it depends and interplays on size, chemical and elastic factors, at the (001) surface of BaTiO3.First-principles calculations, based on density functional theory, have been performed to enlighten the influence of surface terminations, in-plane strain, system thickness and domain size in ultrathin films on the polarization in different ferroelectric phases. The effect of surface oxygen vacancies on the polarization and electronic structure has also been investigated. Low Energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) have been used to study the surface properties of ferroelectric polarization in reduced BaTiO3 single crystals, allowing to address the influence of oxygen vacancies on the ferroelectric polarization from experimental approaches, supporting the calculations results.
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Jelle Dionot. Topology of ferroelectric polarization at the BaTiO3(001) surface from ab initio calculations and electron microscopy-spectroscopy. Other [cond-mat.other]. Université Paris Sud - Paris XI, 2015. English. ⟨NNT : 2015PA112182⟩. ⟨tel-01243180⟩

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