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DF: Dielektrische Festkörper

DF 2: Elektrische und optische Eigenschaften II

DF 2.3: Talk

Monday, March 11, 2002, 15:30–15:50, 11

Dielectric barrier micro-discharges: Microscopic origin for the charging of piezoelectric polymer foams — •Michael Lindner, Reinhard Schwödiauer, Mario Dansachmüller, Simona Bauer-Gogonea, and Siegfried Bauer — Johannes-Kepler Universität, Altenbergerstr. 69, 4040 Linz, Österreich

Piezoelectricity is typically observed in non-centrosymmetric crystals only. Nonpolar materials are therefore excluded as piezoelectric materials. However, recently several groups reported surprisingly large piezoelectricity in corona charged nonpolar polymer foams. So far, the microscopic origin of the charging process is still hidden in the dark.

Here we show that dielectric barrier (silent) micro-discharges are responsible for the charging and for the large piezoelectric responses in polymer foams. Silent micro-discharges are widely used for ozone synthesis, as ultraviolet light source (excimer lamps) and for plasma display panels. In silent micro-discharges, the discharge gap is isolated from the electrodes by dielectric layers. Above the threshold voltage for breakdown of the gap, self-extinguishing micro-discharges that transfer a sheet charge across the air-gap are ignited. Thereby large macroscopic dipoles are formed within the voids of the foam, responsible for the large intrinsic piezoelectric response. The silent discharges are investigated electrically and optically by means of the light emission from the voids during breakdown. Additionally, we show ferroelectric-like behavior in the nonpolar foam materials.

Work supported by the FWF.