Abstract

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 β 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.

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