‘Universal’ curve of ionic conductivities in binary alkali germanate glasses

An analysis and brief discussion of experimental ionic conductivity σ in the binary alkali germanate system is presented, exemplified on 31 binary GeO2 glasses that span ionic conductivity by more than 17 orders of magnitude in a wide composition range. An ‘universal’ finding using modified Arrhenius plots log σ or log σT versus EA/kBT is obtained, where EA is the activation enthalpy for conduction, kB the Boltzmann constant and T is the absolute temperature. For a given value of EA/kBT, the difference between large to small values of σ is only about one order of magnitude in 87% of the glass systems considered. The fact that σ lies on these single ‘universal’ curves for so many ion-conducting binary germanate glasses means that σ is governed mainly by EA while the pre-exponential factor σ0 varies around an average value ≈50 S cm−1. The activation enthalpy composition dependence is explained concerning the Anderson–Stuart theory.