Electrical conductivity relaxation in PVOH–LiClO4–Al2O3

We report on electrical conductivity relaxation measurements of solid polymer electrolytes (SPE) based on poly(vinyl alcohol) (PVOH) and LiClO4 in which nanoporous Al2O3 particles with average pore diameter of 58 Å were dispersed. A power law frequency dependence of the real part of the electrical conductivity is observed as a function of temperature and composition. This behaviour is typical of systems in which correlated ionic motions in the SPE bulk material are responsible for ionic conductivity. This variation is well fitted to a Jonscher expression σ′(ω) = σ0[1 + (ω/ω0)p] where σ0 is the dc conductivity, ω0 the characteristic angular frequency relaxation and p is the fractional exponent between 0 and 1. For a prototype membrane with composition 0.9PVOH − 0.1LiClO4 + 7 wt.%Al2O3, it was found that the temperature dependence of σ0 and ω0, may be described by the VTF relationship, ϕ = ϕ0 exp[−B/(T − T0)], with approximately the same constant B and reference temperature T0, indicating that ion mobility is coupled to the motions of the polymer chains. Moreover, p decreased with increasing temperature, from 0.68 at T = 319 K, to 0.4 at T = 437 K, indicating weaker correlation effects among mobile ions when the temperature is increased.