Ionic tracer diffusion and dc conductivity in the polymer electrolyte PEO30NaI

We studied ion transport in an amorphous mixture of poly(ethylene oxide) (PEO) and sodium iodide with an O-to-Na ratio of 30. Diffusion coefficients were obtained from 22Na and 125I radiotracer experiments in the temperature range from 67 to 180 °C. The results are compared with the dc electrical conductivity originating from frequency-dependent impedance measurements. The observed disparity between the sum of the tracer diffusivities and the charge diffusivity can be accurately described in a model that accounts for the formation of neutral pairs due to association of cations and anions.