Topological Structure-Induced Piezoelectricity from the α-Phase Poly(Vinylidene Fluoride)

Topologically polar structures offer a rich landscape for uncovering emergent phenomena inaccessible in traditional ferroelectric materials. In contrast to the numerous examples found in ferroelectric oxides, topological structures identified in ferroelectric polymers are extremely rare. Here, the creation of a meron-like topological polar structure is demonstrated in the non-polar α-phase poly(vinylidene fluoride) (PVDF). The formation of the twisted lamellae within ring-banded polymer spherulites and the resulting topological structure are revealed using combined experimental and computational methods. Non-zero polarization is demonstrated using Kelvin probe force microscopy, second harmonic generation measurement, and dielectric spectroscopy, and verify the facilitation of polarization orientation by strain in the topological α-phase PVDF. Accordingly, piezoelectricity in the topological α-phase PVDF is demonstrated through both direct and converse measurements and reveals a strong correlation between polarization, the piezoelectric coefficient, and the topological structure. This result offers a new perspective on creating polar topological structures and inducing formerly symmetry-forbidden properties like piezoelectricity in the non-polar phase of ferroelectric polymers.