Berlin 2008 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 12: Dielectric and ferroelectric thin films and nanostructures II

DF 12.8: Talk

Thursday, February 28, 2008, 12:40–13:00, EB 107

Space charge polarization in solid electrolytes — •Björn Martin and Herbert Kliem — Saarland University, Germany

Thin films of polyethylene oxide are investigated as model systems for a solid electrolyte. Plane parallel capacitance structures of these samples show a pronounced relaxational behaviour with a thickness dependent effective dielectric constant in the low frequency range. This behaviour is attributed to a space charge polarization of mobile ions in the material.

With a three-dimensional discrete hopping model, it is possible to describe the dielectric properties of the systems. Here, mobile charges can fluctuate thermally activated over barriers in a multiwell energy structure. If all interactions in the system, especially the attracting interactions between the ions and their image charges in the electrodes, are considered, it can be shown that electrode effects play an important role. Thus, these effects are responsible for a Kohlrausch behavior of the polarization current in the long time range as well as for an increased accumulation of charges at the electrodes.

The space charge distribution, predicted by simulations of the model system, is determined by measurements of the surface potential with a scanning Kelvin probe contactless [1]. Due to the motion of negative mobile ions after application of an electric field a positive space charge region is found near the negative electrode resulting in a strongly nonlinear surface potential. Additionally a charge injection process is observed.

[1] B. Martin, H. Kliem, acc. by IEEE Trans. Dielectr. Electr. Insul.