The glass transition temperature of mixed glass former 0.35Na2O + 0.65[xB2O3 + (1 − x)P2O5] glasses

The mixed glass former effect (MGFE) is defined as the non-linear and non-additive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass former compositions. In this study, sodium borophosphate glasses, 0.35Na2O + 0.65[xB2O3 + (1 − x)P2O5] with 0 ≤ x ≤ 1, have been prepared and their glass transition temperatures (Tg) have been examined as an alternative indicator of the MGFE and as an indicator of changes in the short range order (SRO) structural network units that could cause or contribute to the MGFE. The changes in Tg show a positive non-additive and non-linear trend over the changing glass former fraction, x. The increase in Tg is related to the increasing number of bridging oxygens (BO) in the glass samples, which is caused by the increase in the number of tetrahedral boron, B4, units in the SRO structure.

► Mixed glass former effect of 0.35Na2O + 0.65[xB2O3 + (1 − x)P2O5].
► Glass transition temperature, Tg, shows a positive non-linear and non-additive trend.
► The changes in Tg are dependent on the changes in the number of bridging oxygen.
► Changes in the number of bridging oxygen are caused by the changing ratio of modifier to glass former.