Piezoelectricity in βphase poly(vinylidene fluoride) having a ''singlecrystal'' orientationPoly͑vinylidene fluoride͒ ͑PVDF͒ was crystallized under high pressures on the basis of the pressure-temperature ( P-T) phase diagram obtained recently, and piezoelectric and ferroelectric properties of the resulting films were evaluated. Crystallization in the metastable hexagonal phase appearing at high pressure and temperature below the triple point yielded a film comprising extended chain lamellar crystals of a mixture of ␤ and ␥ forms, the latter of which is transformed into ␤ form by poling at an elevated temperature ͑120°C͒. The poled film exhibits strong piezoelectric effect persistent up to the melting temperature ͑205°C͒. The electromechanical coupling factor k t for the thickness extensional piezoelectric effect is 0.27 at 25°C, the largest value ever found in PVDF. The results of studies on morphology, structure, and thermal properties are also described.

No abstract

No abstract

No abstract