Investigations on conductivity anomalies in Li2O center dot 4MnO(1+x)center dot 4B(2)O(3) glasses

Glassy material Li2O . 4MnO(1+x) . 4B(2)O(3) (0 < x < 0.5) has been prepare d by quenching the melt in air, and its electrical conduction behavior has been studied. Two conductivity anomalies are observed around the glass tran sition temperature. One appears in the dependence of the isothermal conduct ivity vs, the annealing time. This anomaly is attributed to the oxidation o f Mn2+ by oxygen ions penetrating into the glass matrix, leading to the inc rease of the charge carrier density. The other anomaly is observed in the d ependence of the conductivity vs, the temperature for different times of an nealing. The abnormal increase and decrease of the conductivity vs, anneali ng time might result from a complicated structural variation in the glass. Below 200 degreesC, the conductivity obeys an Arrhenius relation. Above 350 degreesC, the formation of crystalline MnBO3 causes a conductivity decreas e by one order of magnitude. The conductivity is enhanced by the redistribu tion of free volume between these two temperatures. (C) 2001 Elsevier Scien ce B.V. All rights reserved.