Ionic Space Charge Relaxation and High Dielectric Permittivity in Polyethylene Oxide

摘要

Thin films of polyethylene Oxide with molecular weights from 6*10~3 to 4*10~5 were prepared from aqueous solutions y a spin technique as AL-PEO-Al structures, or as AL-PEO-Si structures. Dielectric measurements were carried out in a frequency range 3 mHz<=f<=1 MHz in atmoshperes of different relative humidity and at different temepratures. The nominal dielectric permittivity exhibits a remarkable dependence on the sample thickness and the relative humidity. We find a ture volume polarization in the high frequency range and a thermally activated relaxation process in the low frequeny rnage, whose time constant is shifted towards high frequencies with increasing r.h.. It is ocnsidered that due to the absorbed dipolar water molecules chemical bonds within the sample are broken and quasi-free ions are generated. These ions move through the sample to the electrode interfaces and form an ionic space charge. We assume that at the PEO-Al interface an oxide layer is formed, which is impermeable for these ions. The transit times and the drift velovities of the ions are almost independent of the electric field strength in the low-field limit. Therefore we conclude that the movement of the ions can be described by a multiwell potential model, where the transition probability between neighbored wells is thermally activated.