Ferroelectrets Filled with a High Breakdown-Strength Gas

Ferroelectrets (i. e. voided, soft polymer composites with internal bipolar space charges) were prepared by laminating porous spacers between polyproplyene films in gas mixtures containing sulfur hexafluoride $(\mathrm{SF}_{6})$, a gas of higher electric breakdown strength than air. This has the potential to reduce “back discharges”, which occur when the electric field created by the deposited space charges exceeds the breakdown strength of the gas in the void. As a result, significantly higher piezoelectric activity is expected. As shown by hysteresis curves and nonlinear capacitance dilatometry measurements, the SF6-filled samples do indeed exhibit an increased polarization and a $2-3\times$ enhancement in their $d_{33}$ coefficients.