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

Abstract

An analysis and brief discussion of experimental ionic conductivity σ in the binary alkali germanate system is presented, exemplified on 31 binary GeO 2 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 E A/ k B T is obtained, where E A is the activation enthalpy for conduction, k B the Boltzmann constant and T is the absolute temperature. For a given value of E A/ k B T, 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 E A while the pre-exponential factor σ 0 varies around an average value ≈50 S cm −1. The activation enthalpy composition dependence is explained concerning the Anderson–Stuart theory.