Some aspects of piezoelectricity and pyroelectricity in uniaxially stretched poly(vinylidene fluoride)

Abstract

The piezoelectric constant of a uniaxially stretched and polarized poly(vinylidene fluoride) film decreases monotonically with increasing temperature in the range from 65 to 165 °C. After a specimen is cooled under open‐circuit conditions, the thermally stimulated current reverses in sign and exhibits a peak at around the glass‐transition temperature T g . Reversible changes in infrared spectra before and after the poling process suggest that the dipoles in the β crystals of poly(vinylidene fluoride) can be aligned along the direction of an applied electric field. The alignment is strongly influenced by the amorphous region; the coercive field in P‐Ehysteresis curve observed at 50 Hz increases rapidly at around T g . Under a high electric field, the uniaxially stretched poly(vinylidene fluoride) film behaves above T g in the same way as ferroelectricceramics.