Abstract
Ferroelectric, pyroelectric and dielectric properties were investigated for Form IV poly(vinylidene fluoride) (PVDF). We fabricated highly crystalline Form II thin films by spin-casting from acetone or methyl ethyl ketone followed by annealing at 155 °C and then converted into Form IV using a high electric field of 500 MV/m. We observed displacement (D) - electric field (E) hysteresis loop and attendant pyroelectric activity that supported ferroelectric polarization reversal in Form IV PVDF. The highly rounded D-E loop with a coercive field of 240 MV/m suggests that reversal of the dipole component perpendicular to TGTG¯ chain requires very high field and progresses based on step-by-step switching of respective molecules. We also observed similar crystalline relaxations in Form II and IV suggesting that fluctuations of parallel dipoles in TGTG¯ chains were not affected by chain packing. Simultaneous observation of polarization reversal and dielectric relaxation associated with two orthogonal directions (a- and c-axis) of crystallites is interpreted using the tilt angle between of the chain axis and sample surface. Microscopic features are discussed in terms of electric-field-induced and thermally-induced changes in TGTG¯ conformational sequences.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have