The pressure and temperature dependence of piezoelectric and pyroelectric response of poled unoriented phase I poly(vinylidene fluoride)

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Abstract
The hydrostatic piezoelectric coefficient dp and the pyroelectric coefficient py of poled unoriented phase I films were measured at pressures up to 7.0 Kbar and at temperatures from −84 to +48 °C. The pressure dependence of the glasstransition temperature over the same pressure range was also determined. The results obtained for these unoriented films are compared with results obtained previously for oriented films. The effect of the glass transition temperature (Tg) and another transition occurring in the range of pressure and temperature used (Tt) on the piezoelectric and pyroelectric response for both oriented and unoriented films are discussed. At temperatures below Tg,py decreased with increased temperature, while dp showed a shallow maximum so that for both types of response minimum values were obtained at the Tg.