Pressure and temperature dependence of the electromechanical properties of polarized polyvinylidene fluoride films

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Abstract
The piezoelectric resonance method was adopted in order to measure piezoelectric and elastic constants of polyvinylidene fluoride films over the temperature range from −40 to 60 °C and at pressure up to 3 kbar. We have shown that the glass transition temperature increases with pressure, dTg/dP being approximately equal to 17 °C/kbar at atmospheric pressure. We have demonstrated that the electromechanical coupling factor K32 is not independent of temperature. Previous measurements, carried out at atmospheric pressure, which indicated the invariance of K32 with temperature, corresponded to a particular case of more general thermodynamic behavior.