Topological Origins of the Mixed Alkali Effect in Glass

Abstract

The mixed alkali effect, the deviation from expected linear property changes when alkali ions are mixed in a glass, remains a point of contention in the glass community. While several earlier models have been proposed to explain mixed alkali effects on ionic motion, models based on or containing discussion of structural aspects of mixed-alkali glasses remain rare by comparison. However, the transition-range viscosity depression effect is many orders in magnitude for mixed-alkali glasses, and the original observation of the effect (then known as the Thermometer Effect) concerned the highly anomalous temperature dependence of stress and structural relaxation time constants. With this in mind, a new structural model based on topological constraint theory is proposed herein which elucidates the origin of the mixed alkali effect as a consequence of network strain due to differing cation radii. Discussion of literature models and data alongside new molecular dynamics simulations and experimental data are presented in support of the model, with good agreement.

The structure of sodium silicate glass from neutron diffraction and modeling of oxygen‐oxygen correlations

“…Alkali silicate glasses are of scientific interest for their ionic transport properties, and for example it is a longstanding challenge to provide a fully satisfactory explanation of the mixed alkali effect in silicates and other glasses. [3][4] However, despite the fundamental interest in sodium silicate glasses, a detailed understanding of the structural role of sodium in the silicate network is still lacking. For example, it is not well understood how sodium bonds to the bridging and non-bridging oxygens in the glass.…”

“…B NMR 12. In a borate glass, there are two different types of oxygenoxygen distance, (O-O) B3~2 .36 Å within the BO3 units, and (O-O) B4~2 .41 Å within the BO 4 units. Within a BO 3 unit, there are three oxygen-oxygen distances, while there are six oxygen-oxygen distances within a BO 4 unit.…”

Competition Effects during Femtosecond Laser Induced Element Redistribution in Ba- and La-Migration Based Laser Written Waveguides

“…This kind of blocking effect somewhat resembles the so-called mixed alkali effect (MAE) in glasses [35][36][37], although in a very different situation. Please note that in what follows in the comparison with the MAE, we refer not to the presence of Na 2 O and K 2 O as fast diffusing modifiers in the glass compositions.…”

Progress in modeling of glass properties using topological constraint theory

“…However, the physical origin of the effect is not yet fully understood. Wilkinson et al have introduced a new structural model based on topological constraint theory to elucidate the origin of MAE . According to this model, γ constraint (defined in the previous section) is critical in governing the effect.…”

“…The orange line is the prediction from the shift in the angles calculated from simulations and the points are present data from DSC measurements. Reproduced from Ref . [Color figure can be viewed at wileyonlinelibrary.com]…”