Electrical conductivity in glass-forming solid electrolytes: theory and experiment

A theory of the ionic conductivity in polymer electrolytes based on defect diffusion is evaluated using previously published data. Those data include the pressure and temperature variation of the electrical conductivity for poly(dimethylsiloxane-ethylene-oxide) complexed with NaCF3COO. In the defect diffusion model, ion transport is controlled by defects and ion motion occurs when the ion is encountered by a single defect. As temperature is lowered or pressure increases, the number of single defects decreases, thus decreasing the ionic conductivity. Further, there exists a pressure-dependent critical temperature, Tc, below which single defects do not exist. It is shown how the pressure dependence of the conductivity is controlled by the pressure dependence of Tc. The theory is used to predict the variation with temperature of both the apparent activation volume and curvature in plots of the logarithm of the conductivity with pressure.