Dynamic Light Scattering in Mixed Alkali Metaphosphate Glass Forming Liquids
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The Mixed alkali effect (MAE) is an often studied phenomenon, 0ccurring in material containing more than one type of alkali, in which a marked deviation from linear compositional dependence is observed. Previous studies have observed a MAE in properties, like the internal friction and dc conductivity, of mixed alkali materials in the glassy state. A MAE has also been observed in the glass transition temperature (Tg) of mixed alkali materials, suggesting that the mechanism behind the effect must persist into the liquid state. In this work, the mixed alkali effect was studied by performing photon correlation spectroscopy on eleven different compositions of LixNa1-xPO3 liquid. This yielded values of Tg, fragility index and the non-exponentiality of the relaxation. All of these properties exhibited the non-linear compositional variation characteristic of the MAE, with a minimum occurring at the most mixed composition. The variation in Tg is in agreement with literature values. The variation in fragility index is thought to be an artifact of the dip in Tg. The variation in non-exponentiality is expected as a decrease in non-exponentiality suggests a greater diversity in relaxation within the liquid.