Dresden 2009 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 15: Thin Films and Nanostructures II

DF 15.1: Talk

Thursday, March 26, 2009, 10:40–11:00, WIL B321

Interface effects in solid electrolytes — •Björn Martin and Herbert Kliem — Saarland University, Germany

To investigate interface effects, thin films of ion conducting polyethylene oxide (PEO) doped with different salt concentrations are used. Capacitance structures with evaporated Al or Cu electrodes are assembled. An ionic space charge polarization prevails in these systems.

For computer simulations, a three-dimensional discrete hopping model is developed. Negative ions can fluctuate thermally activated over energy barriers in a multiwell potential. The interactions of the ions with the electrodes are considered using the method of images. Also, electrostatic interactions between all ions and between the ions and a positive background charge providing neutrality are considered.

The attractive Coulomb forces between the original charges and the image charges cause a charge accumulation at the electrodes even without applied field as predicted in the simulations. Due to the repulsive forces of these accumulation layers a depletion of mobile charges towards the volume of the sample is found. This charge distribution causes an internal potential with a maximum in the middle of the sample. In the experiment, this potential distribution can be determined using a scanning Kelvin probe which detects the surface potential between the electrodes.

Furthermore, the electrode effects are responsible for the dynamic behavior of the systems like the Kohlrausch behavior of the polarization current and thus the increase of the dielectric permittivity at low frequencies, and the onset of charge injection.