Investigations on conductivity anomalies in Li2O·4MnO1+x·4B2O3 glasses

Glassy material Li2O·4MnO1+x·4B2O3 (0<x<0.5) has been prepared by quenching the melt in air, and its electrical conduction behavior has been studied. Two conductivity anomalies are observed around the glass transition temperature. One appears in the dependence of the isothermal conductivity vs. the annealing time. This anomaly is attributed to the oxidation of Mn2+ by oxygen ions penetrating into the glass matrix, leading to the increase of the charge carrier density. The other anomaly is observed in the dependence of the conductivity vs. the temperature for different times of annealing. The abnormal increase and decrease of the conductivity vs. annealing time might result from a complicated structural variation in the glass. Below 200°C, the conductivity obeys an Arrhenius relation. Above 350°C, the formation of crystalline MnBO3 causes a conductivity decrease by one order of magnitude. The conductivity is enhanced by the redistribution of free volume between these two temperatures.