Non-Arrhenius Ionic Conductivities in Glasses due to a Distribution of Activation Energies

Previously observed non-Arrhenius behavior in fast ion conducting glasses [J. Kincs and S. W. Martin, Phys. Rev. Lett. 76, 70 (1996)] occurs at temperatures near the glass transition temperature, T-g, and is attributed to changes in the ion mobility due to ion trapping mechanisms that diminish the conductivity and result in a decreasing conductivity with increasing temperature. It is intuitive that disorder in glass will also result in a distribution of the activation energies (DAE) for ion conduction, which should increase the conductivity with increasing temperature, yet this has not been identified in the literature. In this Letter, a series of high precision ionic conductivity measurements are reported for 0.5Na(2)S + 0.5 [xGeS(2) + (1 x)PS5/2] glasses with compositions ranging from 0 <= x <= 1. The impact of the cation site disorder on the activation energy is identified and explained using a DAE model. The absence of the non-Arrhenius behavior in other glasses is explained and it is predicted which glasses are expected to accentuate the DAE effect on the ionic conductivity.