Dresden 2014 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 18: Dielectric and ferroelectric thin films

DF 18.1: Vortrag

Mittwoch, 2. April 2014, 16:00–16:20, GER 37

An unexpected depolarization current peak in polyethylene oxide — •Bjoern Martin and Herbert Kliem — Saarland University, Germany

Thin films of polyethylene oxide (PEO) are investigated as model systems for a solid electrolyte. Metal-PEO-metal capacitance structures show a pronounced relaxational behaviour with a thickness dependent effective dielectric permittivity caused by a space charge polarization of mobile ions.

In the experiment it is found that the transient polarization and depolarization currents after application of small field steps follow a power law in the long time range. By using higher fields charge injection during the polarization sets in resulting in nearly constant currents in the long time range. The depolarization currents now show an unexpected maximum in time. The time to the maximum depends on the height of the voltage applied before, the polarization time, the sample thickness, the temperature, and the Li doping.

A discrete three-dimensional model is developed to describe the charge motion. Single charges are regarded. Negative ions can fluctuate thermally activated over energy barriers in a multiwell potential. Positive immobile ions provide charge neutrality. Additionally, electrons can be injected into the system and also be extracted from the dielectric. Interactions of the charges with the electrodes using the method of images and all other electrostatic interactions are considered.

From these simulations it is shown that the appearance of the transient depolarization current maximum is caused by injected electrons.