Mechanically deformable organic ferroelectric crystal with plasticity optimized by fluorination

The ability of plastic deformation exerts in bulk crystals would offer great promise for ferroelectrics to achieve emerging and exciting applications. However, conventional ferroelectric crystals generally suffer from inherent brittleness and are easy to fracture. Here, by implementing fluorination on anion, we successfully design a flexible organic ferroelectric phenylethylammonium trifluoromethanesulfonate (PEA-TFMS) with interesting plasticity in its bulk crystals. To our knowledge, it is the first observation since the discovery of organic ferroelectric crystal triglycine sulfate in 1956. Compared to parent PEA-MS (phenylethylammonium mesylate), fluorination subtly alters ionic orientation and interactions to reorganize dipole arrangement, which not only brings switchable spontaneous polarization but also endows PEA-TFMS crystal with macroscopical bending and spiral deformability, making it a competitive candidate for flexible and wearable devices. Our work will bring inspiration for obtaining mechanically deformable organic ferroelectric crystals toward flexible electronics.