Complex AC impedance, transference number and vibrational spectroscopy studies of proton conducting PVAc-NH4SCN polymer electrolytes

The polymer electrolytes composed of poly (vinyl acetate) (PVAc) with various stoichiometric ratios of ammonium thiocyanate (NH4SCN) salt have been prepared by solution casting method. The polymer-salt complex formation and the polymer proton interactions have been analysed by FT-IR spectroscopy. The conductivity and dielectric measurements are carried out on these films as a function of frequency at various temperatures. The complex impedance spectroscopy results reveal that the high-frequency semicircle is due to the bulk effect of the material. The conductivity is found to increase in the order of 10(-8)-10(-4) S cm(-1) at 303 K with the increase in salt concentration. The ionic transference number of mobile ions has been estimated by Wagner's polarization method and the results reveal that the conducting species are predominantly due to ions. The transient ionic current (TIC) measurement technique has been used to detect the type of mobile species and to evaluate their mobilities. The dielectric spectra show the low-frequency dispersion, which is due to the space charge effects arising from the electrodes. (c) 2004 Elsevier B.V. All rights reserved.