TY - JOUR A1 - Raman Venkatesan, Thulasinath A1 - Smykalla, David A1 - Ploss, Bernd A1 - Wübbenhorst, Michael A1 - Gerhard, Reimund T1 - Tuning the relaxor-ferroelectric properties of Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) Terpolymer films by means of thermally induced micro- and nanostructures JF - Macromolecules : a publication of the American Chemical Society N2 - The effects of thermal processing on the micro- and nanostructural features and thus also on the relaxor-ferroelectric properties of a P(VDF-TrFE-CFE) terpolymer were investigated in detail by means of dielectric experiments, such as dielectric relaxation spectroscopy (DRS), dielectric hysteresis loops, and thermally stimulated depolarization currents (TSDCs). The results were correlated with those obtained from differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and Fourier-transform infrared spectroscopy (FTIR). The results from DRS and DSC show that annealing reduces the Curie transition temperature of the terpolymer, whereas the results from WAXD scans and FTIR spectra help to understand the shift in the Curie transition temperatures as a result of reducing the ferroelectric phase fraction, which by default exists even in terpolymers with relatively high CFE contents. In addition, the TSDC traces reveal that annealing has a similar effect on the midtemperature transition by altering the fraction of constrained amorphous phase at the interphase between the crystalline and the amorphous regions. Changes in the transition temperatures are in turn related to the behavior of the hysteresis curves on differently heat-treated samples. During heating, evolution of the hysteresis curves from ferroelectric to relaxor-ferroelectric, first exhibiting single hysteresis loops and then double hysteresis loops near the Curie transition of the sample, is observed. When comparing the dielectric-hysteresis loops obtained at various temperatures, we find that annealed terpolymer films show higher electric-displacement values and lower coercive fields than the nonannealed sample, irrespective of the measurement temperature, and also exhibit ideal relaxor- ferroelectric behavior at ambient temperatures, which makes them excellent candidates for applications at or near room temperature. By tailoring the annealing conditions, it has been shown that the application temperature could be increased by fine tuning the induced micro- and nanostructures. KW - Annealing (metallurgy) KW - Hysteresis KW - Insulators KW - Phase transitions KW - Polarization Y1 - 2022 U6 - https://doi.org/10.1021/acs.macromol.2c00302 SN - 0024-9297 SN - 1520-5835 VL - 55 IS - 13 SP - 5621 EP - 5635 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Raman Venkatesan, Thulasinath A1 - Wübbenhorst, Michael A1 - Gerhard, Reimund T1 - Structure-property relationships in three-phase relaxor-ferroelectric terpolymers JF - Ferroelectrics N2 - Poly(vinylidenefluoride-trifluoroethylene)-based (P(VDF-TrFE)-based) terpolymers represent a new class of electroactive polymer materials that are relaxor-ferroelectric (RF) polymers and that offer unique and attractive property combinations in comparison with conventional ferroelectric polymers. The RF state is achieved by introducing a fluorine-containing termonomer as a "defect" into the ferroelectric P(VDF-TrFE) copolymer, which reduces the interaction between the VDF/TrFE dipoles. The resulting terpolymer exhibits a low Curie transition temperature and small remanent and coercive fields yielding a slim hysteresis loop that is typical for RF materials. Though the macroscopic behavior is similar to RF ceramics, the mechanisms of relaxor ferroelectricity in semi-crystalline polymers are different and not fully understood yet. Structure-property relationships play an important role in RF terpolymers, as they govern the final RF properties. Hence, a review of important characteristics, previous studies and relevant developments of P(VDF-TrFE)-based terfluoropolymers with either chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) as the termonomer is deemed useful. The role of the termonomer and of its composition, as well as the effects of the processing conditions on the semi-crystalline structure which in turn affects the final RF properties are discussed in detail. In addition, the presence of noteworthy transition(s) in the mid-temperature range and the influence of preparation conditions on those transitions are reviewed. A better understanding of the fundamental aspects affecting the semi-crystalline structures will help to elucidate the nature of RF activity in VDF-based terpolymers and also help to further improve their applications-relevant electroactive properties. KW - Relaxor-ferroelectric (RF) fluoropolymers KW - structure-property KW - relationships KW - Curie transition KW - dielectric hysteresis KW - thermal KW - processing KW - mid-temperature transition(s) Y1 - 2022 U6 - https://doi.org/10.1080/00150193.2021.2014260 SN - 0015-0193 SN - 1563-5112 VL - 586 IS - 1 SP - 60 EP - 81 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Raman Venkatesan, Thulasinath A1 - Smykalla, David A1 - Ploss, Bernd A1 - Wübbenhorst, Michael A1 - Gerhard, Reimund T1 - Non-linear dielectric spectroscopy for detecting and evaluating structure-property relations in a P(VDF-TrFE-CFE) relaxor-ferroelectric terpolymer JF - Applied physics : A, Materials science & processing N2 - Non-linear dielectric spectroscopy (NLDS) is employed as an effective tool to study relaxation processes and phase transitions of a poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) relaxor-ferroelectric (R-F) terpolymer in detail. Measurements of the non-linear dielectric permittivity epsilon 2 ' reveal peaks at 30 and 80 degrees C that cannot be identified in conventional dielectric spectroscopy. By combining the results from NLDS experiments with those from other techniques such as thermally stimulated depolarization and dielectric-hysteresis studies, it is possible to explain the processes behind the additional peaks. The former peak, which is associated with the mid-temperature transition, is found in all other vinylidene fluoride-based polymers and may help to understand the non-zero epsilon 2 ' values that are detected on the paraelectric phase of the terpolymer. The latter peak can also be observed during cooling of P(VDF-TrFE) copolymer samples at 100 degrees C and is due to conduction and space-charge polarization as a result of the accumulation of real charges at the electrode-sample interface. KW - Non-linear dielectric spectroscopy KW - P(VDF-TrFE-CFE) KW - Relaxor-ferroelectric polymer KW - Dielectric hysteresis KW - Curie-transition KW - Mid-temperature transition Y1 - 2021 U6 - https://doi.org/10.1007/s00339-021-04876-0 SN - 0947-8396 SN - 1432-0630 VL - 127 IS - 10 PB - Springer CY - Berlin ; Heidelberg ; New York ER -