Mixed Alkali Effects in Phosphate Glasses

Electrical conductivities, densities, thermal expansion coefficients, glass transition temperatures and softening temperatures were determined for mixed alkali phosphate glasses of the Li2O-Na2O-Al2O3-P2O5, Na2O-K2O-Al2O3-P2O5 and Li2O-K2O-Al2O3-P2O5 systems in which the total alkali content was kept constant. All the three phosphate glass systems exhibited the mixed alkali effect in electrical conduction ; the plots of log (electric conductivity), logσ, versus alkali mixing ratio, R/(R+R\u27), showed a marked minimum at a certain alkali ratio near 1:1, indicating that phosphate glasses behave similarly to silicate and borate glasses regarding the mixed alkali effect. No pronounced effect of presence of two kinds of alkali ions was seen in the density and thermal expansion coefficient. The plots of glass transition temperature, Tg, and softening temperature, Ts, against the alkali mixing ratio a small minimum as is seen in many mixed alkali silicate and borate glasses