Influence of annealing temperature on the existence of polar domain in uniaxially stretched polyvinylidene-co-hexafluoropropylene for energy harvesting applications

The structural and electroactive properties of the as-prepared random copolymer polyvinylidene-co-hexafluoropropylene thin film are explored as a function of thermal treatment at various temperature regions. The thermal treatment of the polymer thin film not only changes the structural conformations that is very natural but establishes a polar domain in the non-polar alpha-phase. Here, we discover an anomalous temperature-dependent crossover behavior from the non-polar alpha-phase to an appreciable enhancement in ferroelectric and piezoelectric responses. The maximum unipolar strain (S-max=-5.01%), an ultrahigh value of normalized piezoelectric coefficient (d(33)*=-556 pm/V), high electromechanical coupling factor (K-p = 0.78) factor including the high dielectric constant (epsilon' = 23 at 100 Hz) at a relatively low electric field of 900 kV/cm may, therefore, be an effect of the established polar domain for the sample annealed at 105 degrees C. The direct piezoelectric charge coefficient (d(33)), a key factor for the performance of a prepared polymer thin film system as an energy harvester, lies in the range of -10 +/- 2 pC/N. Also, the annealed sample exhibited a persistent polarization after several cumulative cycles of applied stress. Published under license by AIP Publishing.