The mixed alkali effect in the MgO-Li2O-Na2O-K2O-B2O3 glass system

The mixed alkali effect (MAE) in a glass system containing three alkali ions (Li, Na and K) is studied. Glasses with the composition 10MgO-(x+y)Li2O-(15-x)Na2O-(15-y)K2O-60B(2)O(3)[X=y=0, 2.5, 5, 7.5, 10, 12.5 & 15 mol%] were prepared using melt quenching. The glassy nature of the samples prepared was confirmed by XRD studies. In the glass system studied the alkaline earth oxide MgO content was kept constant while the content of the three alkali oxides was varied. The Tg values were calculated from differential scanning calorimetry (DSC) thermograms. The DC ionic conductivity was measured at different temperatures. The variation of conductivity followed the Arrhenius relation. The activation energies were calculated from the conductivity plots. The variation of conductivity with Li2O content was nonlinear and exhibited wave shaped curve. This type of variation may be attributed to the mixed alkali effect. The observed results were explained on the basis of the dynamic structure model (DSM) and the MAE observed in the present glass system may be attributed to the interaction between the alkali ions and between the alkali ions and the glass network.