A model interpretation op the correlation between the activation enthalpy and the breath op electric modulus spectrum on varying the compositions in alkali aluminogermanate and other glasses

Abstract

From measurements of both d.c. and a.c. conductivity in wide composition range of alkali aluminogermanate glasses xM 2 O:yAl 2 O 3 :(1 − x − y)GeO 2 where M is the alkali Na or Rb, x ranges from 6 × 10 −4 to 0.29 and y/x −O , 0.33 and 1.0, we have established a correlation between the activation enthalpy E a * for d.c. ionic conductivity and the exponent n in the Kohlrausch function expt/τ * ) 1−n for electric field decay that gives a rather accurate description of both the d.c. and a.c. conductivity data. A similar trend has been observed also by Martin and Angell in Li 2 -P 2 O 5 glasses over the composition range 37–62 mol % Li 2 O − . In this work we shall use the coupling model of relaxation to interpret these results and to provide additional insight into electrical relaxation mechanism. The coupling model has been proven to be successful in explaining several anomalous features observed in vitreous ionic conductors. In varying the composition of a glass system, it does expect the coupling parameter n which appears in the Kohlrausch exponent to increase with decrease in the primitive activation enthalpy E a = (1−n)E a * , in agreement with the empirical correlation observed over a wide composition range. Further spin-lattice relaxation measurements give a direct measure of E a in support of this interpretation. The same correlation is verified also in mixed alkali and fluorinated borate glasses, and these data are explained also by the coupling model.