The Longitudinal and Transverse Piezoelectric Effects of the Ferroelectric Polymer P(VDF-TrFE)

Polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) exhibits outstanding electromechanical properties and is a material of choice for non-volatile memories, energy-harvesting systems, multifunctional actuators, and sensors. However, this polymer remains one of the least understood materials among ferroelectric materials due to its semi-crystalline structure with chains folding in elongated grains through the lamellae and amorphous regions. Here, operando high-resolution X-ray diffraction is exploited to unravel the P(VDF-TrFE) structural evolution upon the first electric field application, called poling. This X-ray technique allows revealing drastic changes in the lamellae with the ordered amorphous (OA) emergence between crystalline nanodomains. The discovery of this OA emergence is critical because it significantly affects the structure, as well as the mechanical, ferroelectric, and piezoelectric properties of the polymer. After poling, even small nanostructural changes lead to measurable effects yielding the piezoelectric coefficients. The longitudinal and transverse piezoelectric effects can be explained by the complex P(VDF-TrFE) structure. The elongated grains consist of lamellae separated by isotropic amorphous (IA) regions. This study not only sheds light on the fundamental mechanisms occurring in P(VDF-TrFE), but also offers guidance for new ferroelectric organic materials for flexible, biocompatible sensor and energy applications.