Six-Fold Vertices in a Single-Component Organic Ferroelectric with Most Equivalent Polarization Directions

Topological defects such as vortices
in ferroelectric materials
are attracting tremendous interest because of their splendid possibilities
for unique physical phenomena and potential applications in nanoelectronic
devices. However, reports of the vortex structure have been scarce
in organic ferroelectrics, which are highly desirable for their mechanical
flexibility, easy and environment-friendly processing, and low acoustical
impedance. Here, we successfully observed the robust triangular domains
in a single-component organic ferroelectric, 2-(hydroxymethyl)-2-nitro-1,3-propanediol
(1), six of which can form a 6-fold vertex domain structure.
To our knowledge, it is the first time that such an intriguing topological
vortex gets experimentally confirmed in ferroelectrics. Moreover,
the symmetry change of 1 with an Aizu notation of m3mF1 leads to the most 48 crystallographically
equivalent polarization directions among all ferroelectrics. With
those benefits and excellent piezoelectric properties, compound 1 shows great potential as a reconfigurable electronic element
or a mechanical sensor for soft robotics, flexible and wearable devices,
and biomachines.