Universal curve of ionic conductivities in binary alkali germanate glasses

Abstract

An analysis and brief discussion of experimental ionic conductivity a 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 sigma or log sigma T 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 or is only about one order of magnitude in 87% of the glass systems considered. The fact that a lies on these single 'universal' curves for so many ion-conducting binary germanate glasses means that or is governed mainly by EA while the pre-exponential factor sigma(0) varies around an average value approximate to 50 S cm(-1). The activation enthalpy composition dependence is explained concerning the Anderson-Stuart theory.