Optical and Electrical Properties of Pure and Doped PEO Polymer Electrolyte Films

A sodium ion conducting polymer electrolyte based on polyethylene oxide (PEO) complexed with NaFeF4 was prepared using solution cast technique. The complexation of the salt with PEO was confirmed by X‐ray diffraction (XRD) and infared spectroscopic (FTIR) studies. Optical absorption studies were made in the wavelength range 200–600 nm on pure and NaFeF4 doped PEO film. The absorption edge was observed at 4.62 eV for undoped PEO while it ranged from 3.86 to 3.61 eV for NaFeF4 doped films. The direct band gaps for undoped and NaLaF4 doped PEO films were found to be, respectively, 4.54 and 3.74, 3.63 and 3.54 eV while the indirect band gaps were 4.43 and 3.52, 3.38 and 3.26 eV, respectively. It was found that the energy gaps and band edge values shifted to lower energies on doping with NaFeF4 salt. Electrical measurements were made in the temperature range 300–370 K as a function of dopant concentration. The nature of charge transport in this system was determined using Wagner's polarization technique and was found to be predominantly due to ions.