Non-Debye conductivity relaxation in a mixed glassformer system

The electrical conductivity and conductivity relaxation of different network glasses (Na2O)(0.2)-(GeO2)(0.8), (Na2O)(0.2)-(TeO2)(0.8) and (Na2O)(0.2)-(TeO2)(0.4)-(GeO2)(0.4) have been investigated as a function of frequency and temperature. Conductivity relaxation data are presented using electrical modulus formalism. Conductivity relaxation in these glasses is found to be non-Debye as the value of stretched exponent beta is smaller than one. The microscopic activation energy E-a is determined using the coupling model. It is seen that there is a correlation between E-a and beta. This and the fact that these glasses have different structure, suggest that the depth of the potential in which the mobile ion resides, plays an important role in deciding the conductivity relaxation. The compositional dependence of beta is also discussed in terms of their glass transition temperatures. (c) 2005 Elsevier B.V. All rights reserved.