Comparisons of ferroelectric and dielectric behavior of polyvinylidene fluoride and polyvinylidene fluoride trifluoroethylene

We investigate the crystal properties dependence of the dielectric and ferroelectric performance of pure polyvinylidene fluoride (PVDF) films with various molecular weights using large-scale stretching of 5-time. After stretching, all PVDF films show the crystalline transition from well-defined α and γ crystal grains to all trans crystal slice rather than transition from α to β phase that of commonly think. Therefore, the dielectric response of all trans dipoles in PVDF enhances since the crystal grains are destroyed and well-folded restricted molecule chains are straightened. However, stretched PVDF films not appear a normally ferroelectric but an unsaturated ferroelectric behavior even under 200 MV /m above the coercive electric field, which is very different from the copolymer polyvinylidene fluoride trifluoro ethylene (P(VDF-TrFE)). For its typical character of ferroelectricity, P(VDF-TrFE)70/30mol.% show the high maximum and remnant displacements (15μC/cm²and 10.5 μC/cm²), which are far larger than that of stretched PVDF (7.9μC/cm²and 1-4 μC/cm²depending on molecular weight). This result is significance to clarify the dependence of ferroelectric behavior one crystalline monography of PVDF and P(VDF-TrFE) and thereby, regulate its applications in dielectric and piezoelectric devices.