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P(VdF-HFP) films are fabricated via a solution casting doctor blade method using high (HVS) and low (LVS) volatile solvents, respectively. The structural properties and the ferroelectric behavior are investigated. The surface structure and crystal phase composition are found to be strongly dependent on the type of solvent. LVS leads to a rougher copolymer surface structure with large spherulites and a lower crystallinity in contrast with HVS. The crystalline phase of copolymer films fabricated with HVS consists almost exclusively of α-phase domains, whereas films from LVS solution show a large proportion of γ-phase domains, as concluded from Raman and X-ray diffraction spectra. Virgin films show no ferroelectric (FE) switching polarization at electric field amplitudes below 180 MV/m, independent of the solvent type, observed in bipolar dielectric displacement-electric field measurements. After applying electric fields of above 180 MV/m, a FE behavior emerges, which is significantly stronger for LVS films. In a repeated measurement, FE polarization switching already occurs at lower fields. A shielding effect may be related to this observation. Additionally, Raman bands of polar γ-phase increase by high-electric-field cycling for the LVS sample. The solvent used and the resulting crystal phase composition of the virgin sample is crucial for the copolymer behavior during bipolar electrical cycling.

Ferroelectric polymers are promising as piezoelectric sensors and devices for data storage, energy harvesting and fast energy storage. However, efficient electric polarization as well as piezoelectric and dielectric responses of as-deposited films are often much lower than expected in a crystalline model, because the local orientations of electric dipoles show substantial disorder. Here we introduce an approach for in-plane alignment of the polarization based on applying soft mechanical pressure with a force microscopy tip. Micron-sized ferroelectric domains with well-defined in-plane and out-of-plane polarization orientation and low surface roughness have been written in poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) films on graphite. Inside such domains, the piezoelectric response is more than four times that of the untreated film. The achieved polarization alignment can advance the performance of many devices, since it reduces the cancellation of local responses to electric fields or mechanical strains resulting from polarization disorder., New Journal of Physics, 20, ISSN:1367-2630