ARRHENIUS AND NON-ARRHENIUS CONDUCTIVITIES IN INTERCALATED POLYMER ELECTROLYTES

Intercalated polymer electrolytes (IPEs), Cd(0.75)PS(3)A(0.5)(PEO) [A = Li, Na, K, Cs], formed by the insertion of alkali metal ions solvate d by polyethylene oxide (PEO) into the interlamellar space of the laye red insulating cadmium thio-phosphate form an interesting class of mat erials. Their ambient temperature dc conductivities are comparable to that of the corresponding solid polymer electrolytes (SPEs) formed by dissolving alkali-metal salts in PEG. The conductivity of the intercal ated materials, irrespective of the cation, exhibits a change in condu ction mechanism with temperature. At low temperatures (T < 225 K) the dc conductivity values are small and exhibit an Arrhenius temperature dependence. Above 225 K the dc conductivity rises sharply and in this temperature regime its temperature variation depends on the alkali-cat ion. The dc conductivity of the Li and Na containing IPEs follow the n on-Arrhenius Vogel-Tamann-Fulcher (VTF) relation, sigma(dc) = sigma(0) T(-0.5) exp(-B/(T - T-0)), while the K and Cs IPEs follow an Arrhenius dependence. The origin of the Arrhenius and non-Arrhenius conductivit y of the IPEs, Cd(0.75)PS(3)A(0.5)(PEO) [A = Li, Na, K, Cs], have been investigated by analyzing the frequency-dependent conductivity in the dielectric and electrical modulus representations. We show that the d ifference in behavior is related to differences in the coupling of ion ic motion and polymer segmental modes. In the Li and Na containing IPE s the motions are coupled and the conductivity exhibits a VTF temperat ure dependence. In the K and Ca compounds these motions are decoupled, consequently, although the mean relaxation time associated with segme ntal motion of the intercalated PEO exhibits a VTF dependence, ionic c onductivity has an Arrhenius temperature dependence. (C) 1998 American Institute of Physics. [S0021-9606(98)52241-6]