Intersecting multiaxial domain walls in plastic ferroelectric crystal films

Plastic ferroelectrics comprise a class of solution-processable molecular ferroelectrics, in which spherical polar molecules can rotate and/or freeze within crystal lattices. Some compounds exhibit superior multiaxial ferroelectricity and very sharp ferroelectric switching characteristics, although the domain wall (DW) character-istics have not yet been explored. Here, we report distinctive DW characteristics in drop-casted monocrystalline thin films of a typical plastic/ferroelectric [AH][ReO4]. We demonstrate that the films form 71 degrees, 109 degrees, and 180 degrees DWs, unique to the pseudocubic rhombohedral lattice, that emerge and compete with each other, depending on the crystallographic orientation of the films. Particularly, it is observed that all three types of DWs intersect at several single points, whose unique nature should be ascribed to the small elastic deformation. The observed domains and 180 degrees DWs also comprise much larger periodicity and scaling than those of conventional inorganic ferroelectric films, which should be associated with the unique polarization reversal mechanism in the compound films. These observed features reveal the exotic multiaxial ferroelectricity of soft plastic/ferroelectrics, paving the way for developing printable ferroelectronics.