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Séminaires

jeudi 18 avril 2019 à 14H00
CINaM - Salle Raymond Kern
Salia Cherifi-Hertel
Université de Strasbourg, IPCMS UMR7504
Topology of Domain Walls in Ferroelectric Materials

Abstract
The properties of domain walls in ferroelectric systems can significantly differ from those of the adjacent domains. Such local changes of the material properties could result from a peculiar organization of the polarization at the core of the walls. Recent theoretical studies have shown that even in the simplest case of nominally uncharged 180° ferroelectric walls, which were originally assumed to display Isin g-type configuration, a Néel or Bloch-type internal structure can exist. The possibility of ferroelectric systems to develop such non-Ising domain walls is now well-established, but their experimental observation is challenged by the difficulty to detect the polarization configuration in an extremely narrow region, since the domain wall width typically extends only over a few atomic cells.

We use local second-harmonic generation (SHG) polarimetry, and numerical simulations exploiting symmetry considerations, to probe ferroelectric domain walls in thin epitaxial films as well as in three-dimensional (3D) bulk crystals. In this talk, I will first demonstrate the existence of polarization component within the 180° wall regions separating c-domains in uniaxial ferroelectric systems [1]. Deviations from the ideal Ising configuration, and a Néel-type internal structure are evidenced in tetragonal Pb(Zr,Ti)O3 thin films. As an independent test of our approach, we investigate a periodically poled trigonal LiTaO3 bulk crystal in which theoretical studies predict Bloch-type walls. In spite of significant differences between the two systems (i.e., film vs. bulk, 3m vs. 4mm symmetry), a deviation from the Ising configuration is also observed in Y-oriented walls, with predominant Bloch-type configuration. This corroborates recent theoretical predictions of a more complex, often chiral domain wall structure. Possible origins of the deviation from the Ising configuration will be discussed based on recently reported studies of various systems, including morphotropic phase boundaries in bulk crystals [2], tilted walls [3], and twin boundaries [4].

References

[1] S. Cherifi-Hertel et al., Nat. Commun. 8, 15768 (2017).
[2] X.-K. Wei et al., Nat. Commun. 7, 12385 (2016).
[3] G. De Luca et al., Adv. Mater. 29, 1605145 (2017).
[4] A.N. Morozovska et al., Phys. Rev. B 85, 94107 (2012).

Invitation : - Entrée libre