Enhanced Piezoelectricity in Stretched Relaxor Ferroelectric Polymers Near the Morphotropic Phase Boundary

Morphotropic phase boundary (MPB) acting as a versatile tool has been used to improve the weak piezoelectric coefficients of ferroelectric polymers. However, there remain very few polymers exhibiting MPB, which are often induced by a conventional compositional approach. Here, the existence of the MPB in relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymers is reported, expanding the library of the MPB family. Moreover, it is found that without changing the composition, the relative stability between different crystalline phases, crystallinity, and crystallite size can be manipulated by varying the polymer processing conditions. A markedly enhanced piezoelectric coefficient d33 of −85.2 pC N−1 was obtained in terpolymers fabricated by combined uniaxial stretching and thermal annealing, corresponding to more than a twofold improvement over the untreated counterpart. This work therefore provides an alternative degree of freedom to optimize piezoelectric coefficients for polymer compositions close to MPB, which paves the way toward the scalable fabrication of high-performance ferroelectric polymers for flexible and wearable piezoelectric applications.