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Polarization Orientation, Piezoelectricity, and Energy Harvesting Performance of Ferroelectric PVDF-TrFE Nanotubes Synthesized by Nanoconfinement



1D nanostructures of soft ferroelectric materials exert promising potential in the fields of energy harvesting and flexible and printed nanoelectronics. Here, improved piezoelectric properties, energy-harvesting performance, lower coercive fields, and the polarization orientation of poly(vinylidene fluoride–trifluoroethylene) (PVDF-TrFE) nanotubes synthesized with nanoconfinement effect are reported. X-ray diffraction (XRD) patterns of the nanotubes show the peak corresponding to the planes of (110)/(200), which is a signature of ferroelectric beta phase formation. Piezoforce spectroscopy measurements on the free-standing horizontal nanotubes bundles reveal that the effective polarization direction is oriented at an inclination to the long axis of the nanotubes. The nanotubes exhibit a coercive field of 18.6 MV m−1 along the long axis and 40 MV m−1 (13.2 MV m−1 considering the air gap) in a direction perpendicular to the long axis, which is lower than the film counterpart of 50 MV m−1. The poled 200 nm nanotubes, with 40% reduction in poling field, give larger piezoelectric d33 coefficient values of 44 pm V−1, compared to poled films (≈20 pm V−1). The ferroelectric nanotubes deliver superior energy harvesting performance with an output voltage of ≈4.8 V and power of 2.2 μW cm−2, under a dynamic compression pressure of 0.075 MPa at 1 Hz.