Domain walls (DWs) in ferroelectrics are nm-sized local topological two-dimensional defects that separate regions of uniform polarization. Under an external stimulus such as an electric or mechanical field, the walls move and contribute significantly to the macroscopic response of ferroelectrics [1]. Transmission electron microscopy (TEM) methods have made it possible to study their structure, chemical composition, chirality, the nature of defects segregating (e.g., vacancies at cationic or anionic sites), and strain field distribution thus understanding the local structure of DWs under defined equilibrium conditions [2-4]. However, DWs dynamics under external stimulus has been studied to a lesser extent, particularly with respect to defect segregation, strain and charge field distribution at DWs. The latter is also important when domain walls are used as functional components in nanoelectronics [5].
 
In this presentation we will focus on the dynamics of DWs under applied voltage in BiFeO3 - and (K,Na)NbO3 - based ferroelectrics using Cs-probe-corrected scanning TEM (Cs-STEM) with an is situ biasing STEM holder. We will present results on different types of DWs, e.g., nanodomains in KNN-based or zigzag, and lamellar, charged, and uncharged walls in BiFeO3-based materials [6]. We will obtain information about polarization indirectly from the displacement of the B-site atoms with respect to the center of the A-site sublattice or directly using recently introduced high-speed pixelated direct electron detectors (4D STEM). We will show that the dynamics of domain walls, in the presence of defects, reveals unique and complex phenomena down the atomic level, and involves a change in the distribution of defects, changes in the bound charge distribution, a distortion of the unit cell, and thus a redistribution of strain at DWs under electrical stimuli.
 
 
References:
[1] Fancher, C.M.; Brewer, S.; Chung, C.C.; Röhrig, S.; Rojac, T.; Esteves, G.; Deluca, M.; Bassiri-Gharb, N.; Jones, J.L., Acta Materialia, 2017, 126, 36-43
[2] Rojac, T.; Ben?an, A.; Draži?, G.; Sakamoto, N.; Urši? Nemevšek, H.; Jan?ar, B.; Tav?ar, G.; Makarovi?, M., Walker, J.; Mali?, B., Damjanovi?, D., Nat. Mater., 2017, 16, 3, 322-327
[3] Condurache, O.; Draži?, G.; Sakamoto, N.; Rojac, T.; Ben?an, A., J. Appl. Phys., 2021, 129, 5, 054102-1-8
[4] Ben?an, A.; Draži?, G.; Urši? Nemevšek, H.; Makarovi?, M.; Komelj, M.; Rojac, T., Nat. Commun., 2020, 11, 1762-1-1762-8
[5] Nataf, G. F.; Guennou, M.; Gregg, J. M.; Meier, D.; Hlinka, J.; Salje E. K. H.; Kreisel J., Nat. Rev. Phys., 2020, 2, 634-648
[6] Condurache, O; Draži?, G.; Rojac, T.; Urši? Nemevšek, H.; Dkhil, B.; Bradeško, A.; Damjanovi?, D.; Ben?an, A., Nano Lett., 2023, 23, 750-756