Regensburg 2002 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 9: Blockcopolymere, Blends und Kompositmaterialien

CPP 9.7: Vortrag

Dienstag, 12. März 2002, 15:30–15:50, H38

Can nonpolar materials be No-dqferroelectricNo-dq? — •Reinhard Schwödiauer, Michael Lindner, Mario Dansachmüller, Simona Bauer-Gogonea, and Siegfried Bauer — Johannes-Kepler Universität, Altenbergerstr. 69, 4040 Linz, Österreich

In the generally accepted definition, ferroelectricity is observed solely in pyroelectric crystals. Ferroelectric crystals show two thermodynamically stable states for the spontaneous polarization, that can be switched by means of an electric field. However, besides the spontaneous polarization, ferroelectric materials also show pyro- und piezoelectricity, the linear electro-optical Pockels effect, as well as other second-order nonlinear optical effects.

Nonpolar materials are typical examples of non-ferroelectric materials, since they do not exhibit spontaneous polarization. However, here we show that composites made of nonpolar materials, e.g. polymer and air (polymer foams) exhibit effects that have been observed up to now solely in ferroelectric materials: hysteresis of the dielectric displacement, the mechanical strain, as well as of the linear electro-optical effect and the frequency doubling of light! From this point of view, even composites made e.g. of Teflon and air can exhibit ferroelectric features! The microscopic mechanism behind these observations are silent micro-discharges within the voids of the composites. In contrast to traditional ferroelectric materials, the No-dqspontaneous polarizationNo-dq in these composites is metastable, however, with lifetimes on the order of years or decades at room temperature.

Work supported by the FWF.