MIXED-ALKALI EFFECT IN TELLURITE GLASSES AND CHANGE IN FRAGILITY

The mixed alkali effect on the thermal stability, viscosity, electrica l and dielectric properties was observed in (20-x) Li2O.xNa(2)O.80TeO( 2) glasses. The thermal stability in the glass with Li2O/Na2O=1 is ext remely large. The activation energy, E(eta) for viscous flow at glass transition region decreases rapidly due to a mixing of Li2O and Na2O: E(eta)=595 kJ mol(-1) for 20Li(2)O.80TeO(2) and E(eta)=418 kJ mol(-1) for 10Li(2)O.10Na(2)O.80TeO(2). Negative deviations from additivity in the electrical conductivity at 200 degrees C and the relative permitt ivity, and dielectric loss at room temperature in 1 kHz indicate that the mobility of Li+ and Na+ in alkali tellurite glasses also decreases due to a mixing of alkali ions; mixed alkali glasses are less fragile or more strong than single alkali glasses.