Piezoelectric properties of ferroelectric polymers at low temperatures

The piezoelectric properties of PVDF and its co-polymers, P(VDF-TrFE) and P(VDF-TeFE), are studied in a temperature range from room temperature down to 10 K by the piezoelectric resonance method. Although sound velocity and dielectric constants of these films depend strongly on temperature, the electromechanical coupling factor K_t remains essentially constant int he temperature range examined; the value of K_t at 10 K is 0.29 for P(VDF-TeFE), 0.18 for PVDF, and 0.15 for P(VDF-TeFE). The temperature-independent K_t is discussed in terms of the electrostriction, with the electrostriction coefficient observed to be almost independent of temperature. Two examples are described to show that P(VDF-TrFE) transducers work efficiently even at very low temperatures