Broad-Band Conductive Spectra of Polypropylene Oxide Complexed with LiClO4

Abstract

Broad-band conductive spectroscopy covering a 10 mHz–1 GHz frequency range has been employed to examine the ionic motions in polypropylene oxide (PPO) complexed with 0–1% LiClO4 at temperatures from -60 °C to 100 °C. The dc conduction appears as a plateau of the conductive spectra in their medium frequency range. As the frequency is lowered, the dc conduction is suppressed by the electrode polarization and results in a Cole-Cole conductive relaxation. At high frequencies, the conductive spectra are overtaken by the dielectric relaxations due to dipolar motions associated with the segmental- and normal-mode processes of PPO molecules. In addition, a new relaxation process was found, which is attributable to the ionic motion because the relaxation strength increases with LiClO4 concentration in parallel with an increase of dc conductivity. This finding suggests that the dissociated ions undergo local fluctuational motion (ionic relaxation) prior to starting long-range diffusion (dc conduction). Analysis based on a dynamic bond percolation theory shows that this ionic relaxation occurs in harmony with segmental-mode motion while the dc conduction is associated with the normal-mode process through a renewal of local hopping probabilities.