Paper published as part of the special topic on Domains and Domain Walls in Ferroic Materials DDWFM2021 This paper was selected as an Editor's Pick ARTICLES YOU MAY BE INTERESTED IN Contributions to polarization and polarization switching in antiphase boundaries of SrTiO 3 and PbZrO 3

Application of scanning probe microscopy techniques such as piezoresponse force microscopy (PFM) opens the possibility to re-visit the ferroelectrics previously studied by the macroscopic electrical testing methods and establish a link between their local nanoscale characteristics and integral response. The nanoscale PFM studies and phase field modeling of the static and dynamic behavior of the domain structure in the well-known ferroelectric material lead germanate, Pb 5 Ge 3 O 11 , are reported. Several unusual phenomena are revealed: 1) domain formation during the paraelectric-to-ferroelectric phase transition, which exhibits an atypical cooling rate dependence; 2) unexpected electrically induced formation of the oblate domains due to the preferential domain walls motion in the directions perpendicular to the polar axis, contrary to the typical domain growth behavior observed so far; 3) absence of the bound charges at the 180° head-to-head (H-H) and tail-totail (T-T) domain walls, which typically exhibit a significant charge density in other ferroelectrics due to the polarization discontinuity. This strikingly different behavior is rationalized by the phase field modeling of the dynamics of uncharged H-H and T-T domain walls. The results provide a new insight into the emergent physics of the ferroelectric domain boundaries, revealing unusual properties not exhibited by conventional Isingtype walls.

Ferroelectrics have become indispensable in the development of energyefficient oxide electronics. Their domain state is closely linked to the final device functionality, making domain engineering in technology-compatible thin films of paramount importance. Here we demonstrate the local control of domain formation in two-dimensional epitaxial ferroelectric films using structural defect engineering through the substrate topography. Using a combination of first-principles calculations, atom probe tomography, and scanning probe microscopy, we show that out-of-phase boundaries induced at the substrate step edges combined with local off-stoichiometry trigger the formation of ferroelectric domain walls in the layered ferroelectric Bi 5 FeTi 3 O 15 Aurivillius thin films. The substrate treatment and the miscut angle selection allow for precise control of domain size and location in both single layers and multilayer architectures. With this work, we establish a new route for ferroelectric domain engineering and stabilization of functional domain walls in ultrathin ferroelectric layers.

The physical properties of semiconductors are controlled by chemical doping. In oxide semiconductors, small variations in the density of dopant atoms can completely change the local electric and magnetic responses caused by their strongly correlated electrons. In lightly doped systems, however, such variations are difficult to determine as quantitative 3D imaging of individual dopant atoms is a major challenge. We apply atom probe tomography to resolve the atomic sites that donors occupy in the small band gap semiconductor Er(Mn,Ti)O3 with a nominal Ti concentration of 0.04 at. %, map their 3D lattice positions, and quantify spatial variations. Our work enables atomic-level 3D studies of structure-property relations in lightly doped complex oxides, which is crucial to understand and control emergent dopant-driven quantum phenomena.

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