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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 20: POSTER: Biological Systems + New Materials
CPP 20.16: Poster
Mittwoch, 28. März 2007, 16:00–18:30, Poster B
In–situ measurement of the inverse piezoelectric coefficient in ferroelectrets — •Xunlin Qiu, Axel Mellinger, Michael Wegener, Werner Wirges, Guggi Kofod, and Reimund Gerhard — Universität Potsdam, Institut für Physik, 14469 Potsdam, Germany
A number of cellular polymer–ferroelectret materials were discovered to exhibit a strong piezoelectric response after proper charging [1]. The effective polarization (i.e., the density of macroscopic dipoles) in ferroelectrets originates from barrier discharges within the voids which are initiated when the charging voltage exceeds a threshold value. In the present work, the build–up of the effective polarization of ferroelectrets under suitable voltage waveforms was studied by acoustic measurements of the inverse piezoelectric effect. The radiated sound signal has a contribution not only from the effective charge density, but also from the Maxwell stress. Therefore, a “butterfly” curve for the sound signal was obtained during charging under linearly increasing or decreasing voltages. The absolute piezoelectric d33 coefficients were determined by dielectric resonance spectroscopy immediately after charging. By comparing these d33 values with the zero–field sound signals, all other sound–signal measurements were converted to piezoelectric coefficients. A polarization–voltage (P–V) hysteresis loop was obtained by analyzing the data in light of an existing model for the piezoelectric d33 coefficient of ferroelectrets [2].
[1] S. Bauer, R. Gerhard–Multhaupt, G. M. Sessler, Phys. Today 57, 37 (2004).
[2] M. Paajanen, J. Lekkala, H. Välimäki, IEEE–TDEI 8, 629 (2001).