Enhancement of the piezoelectric coefficient in PVDF-TrFe/CoFe2O4 nanocomposites through DC magnetic poling

In the last years flexible, low-cost, wearable, and innovative piezoelectric nanomaterials have attracted considerable interest regarding the development of energy harvesters and sensors. Among the piezoelectric materials, special attention has been paid to electroactive polymers such as poly(vinylidene fluoride) (PVDF) and its copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFe), which is one of the most extensively investigated piezoelectric polymers, due to the high β phase content resulting from specific curing or processing conditions. However, to obtain a high piezoelectric coefficient (d33) alignment of the β phase domains is needed, which is usually reached through applying a high electric field at moderate temperatures. This process, usually referred to as electrical poling, requires the deposition of contact electrodes on the sample surface and the use of high-voltage apparatus. In the present work, in order to overcome these constraints, we have produced, characterized, and studied a polymer nanocomposite consisting of CoFe2O4 nanoparticles dispersed in PVDF-TrFe with enhancement of the β phase alignment through an applied DC magnetic field. The magnetic poling was demonstrated to be particularly effective, leading to a piezoelectric coefficient d33 with values up to 39 pm/V. This type of poling does not need the use of a top electrode or of high magnetic fields (the maximum value of d33 was obtained at 50 mT, using a current of 0.4 A) making the PVDF-TrFE/CoFe2O4 nanocomposite suitable for the fabrication of highly efficient devices for energy harvesting and wearable sensors.