Electromechanical Behavior Of Two Phase Non Percolative Composites: Comparison Between Carbon Black / Polyurethane And PZT / Polyurethane Films

In this study, electric field-induced thickness strain of pure polyurethane (PU), carbon black C/PU composite and ferroelectric PZT/PU composite have been compared. The three compositions have been submitted to whether a bipolar electric field (0.1 Hz), whether a voltage step. Both C and PZT loading improves the strain of the pure polymer matrix. However, PZT filling yields the highest dynamic strain amplitude (-8.1%) achieved for a field of 13.3 kV/mm. For a given field value, the static strain amplitude obtained after a voltage step is nearly equal to the dynamic strain amplitude. The measurement of voltage step-induced current allowed to determine the constant current-voltage (I-V) characteristics of the three compositions and revealed that predominant space charge limited current occurs in the PZT/PU, whereas three different charge transport mechanisms are activated in the pure and C/PU films, depending on the voltage range. These two distinct electrical behaviors may indicate a difference in the trapping ability owing to the presence of shallow traps in PZT/PU and deeper traps in C/PU and especially in pure PU, which could be at the origin of the larger deformations observed for PZT/PU.