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As a model system for solid polymer electrolytes thin polyethylene oxide (PEO) films (0.6-30 µm) are prepared as A1-PEO-A1 and as A1-PEO-Si structures with blocking electrodes. Dielectric measurements (capacitance and loss angle) are carried out in a frequency range of 3 mHz ≤ f ≤ 1 MHz in atmospheres of different relative humidities (0%-75%) and at different temperatures (293-313 K). The nominal permittivity varies from 4 at high frequencies to up to 150 000 at low frequencies. We find true volume polarization in the high frequency range and a thermally activated space charge relaxation process in the low frequency range. Its time constant exhibits a remarkable dependence on the sample thickness, the relative humidity, the ion concentration, and the temperature. Due to the absorbed dipolar water molecules the activation energy of this process is decreased, leading to higher mobility of the ions. An increase in ion concentration also leads to a lower activation energy. The ions are able to move through the sample to the electrode interfaces and build up ionic space charge. We assume that at the interfaces oxide layers are formed, and these are almost impermeable to these ions. The space charge relaxation process has a broad frequency spectrum. The imaginary part of the nominal permittivity [Multiple line equation(s) cannot be represented in ASCII text e has a slope of β = -0.8 to 0.7 above the main relaxation frequency. In the time domain, after application of a voltage step a Kohlrausch behavior of the relaxation current is found. In the short time range we find a current of j ∞ t[sup -0.3] and in the long time range we find j ∞ t[sup -1.1]. A comparison of the frequency and the time domain by Fourier transform shows that the space charge relaxation process is time invariant for small applied voltages. Nonlinear properties that appear at higher voltages are investigated in the frequency domain and in the time domain. [ABSTRACT FROM AUTHOR]

Electrode effects can play an important role in ion-conducting polymers in which a space charge polarization of mobile internal ions prevails. The ions are shifted in an external field and they are attracted to the electrodes due to Coulomb forces caused by their own image charges. These image charges influence the static and dynamic charge distribution. This can be proved experimentally by measurements of the transient surface potential with the scanning Kelvin probe using polyethylene oxide doped with lithium perchlorate (PEO-LiClO4). Simulations performed with a three-dimensional hopping model coincide with the experimental results qualitatively. [ABSTRACT FROM AUTHOR]

Using the scanning Kelvin probe the potential distribution on the surface of an ion-conducting polymer (polyethylene oxide) can be determined. Due to space charge accumulations a voltage applied between two electrodes causes a strongly nonlinear potential distribution in the samples. The curvature of the potential distribution indicates negative mobile ions in the samples. During the measurement the dc currents in the samples are observed to verify the steady state of the potential distribution. Additionally the measurement results are compared to simulations performed with a three-dimensional hopping model. These simulations show qualitatively the same results as the experiments. [ABSTRACT FROM AUTHOR]

The space charge distribution and therefore the distribution of the internal potential in ion-conducting polymers can strongly be influenced by electrode effects. Due to image forces the electrodes attract mobile ions to the electrolyte/electrode interface. Simulations performed with a three-dimensional hopping model yield a charge accumulation of mobile ions at the electrodes as well as a depletion zone near this accumulation layer even without external applied field. The resulting potential shows a maximum in the middle of the sample. Measurements of the surface potential performed with a scanning Kelvin probe using polyethylene oxide confirm the model. [ABSTRACT FROM AUTHOR]