Structure Dependence of Poisson's Ratio in Cesium Silicate and Borate Glasses

In glass materials, Poisson's ratio (ν) has been proposed to be correlated with a variety of features, including atomic packing density (C_g), liquid fragility (m), and network connectivity. To further investigate these correlations in oxide glasses, here, we study cesium borate and cesium silicate glasses with varying modifier/former ratio given the difference in network former coordination and because cesium results in relatively high ν compared to the smaller alkali modifiers. Within the binary glass series, we find positive correlations between ν on one hand and m and C_g on the other hand. The network former is found to greatly influence the correlation between ν and the number of bridging oxygens (n_BO), with a negative correlation for silicate glasses and positive correlation for borate glasses. An analysis based on topological constraint theory shows that this difference cannot be explained by the effect of superstructural units on the network connectivity in lithium borate glasses. Considering a wider range of oxide glasses from the literature, we find that ν generally decreases with increasing network connectivity, but with notable exceptions for heavy alkali borate glasses and calcium alumino tectosilicate glasses.