Enhancing proton mobility and thermal stability in phosphate glasses with WO 3 : the mixed glass former effect in proton conducting glasses.

This study aimed to investigate the impact of WO 3 on the thermal stability of glass, as measured by the glass transition temperature ( T g ), as well as the activation energy ( E a ) of proton conduction and proton mobility ( μ H ). These parameters were analyzed based on variations in the glass network structure and the nature of the P-O and O-H bonds in 35HO 1/2 - x WO 3 -8NbO 5/2 -5LaO 3/2 -(52 - x ) PO 5/2 ( x = 2, 4, 6, and 8) glasses. As previously predicted by a linear regression model, replacing PO 5/2 with WO 3 resulted in an increase in T g and μ H at T g . The observed enhancement rates were +9.1 °C per mol% of WO 3 for T g and 0.09 per mol% of WO 3 for log( μ H at T g [cm 2 V -1 s -1 ]), which aligned with the predicted values of +6.5 °C and 0.08, respectively, validating the linear regression model. The increased T g was attributed to the formation of heteroatomic P-O-W linkages that tightly cross-linked the phosphate chains. The decrease in E a and increase in μ H at T g with increasing WO 3 content were attributed to the reduction of the energy barrier for inter-phosphate chain proton migration owing to the increasing proton migration paths through P-O-W linkages. This μ H enhancement is distinct from previously reported ones due to the reduction of the energy barrier for proton dissociation from OH groups. This phenomenon can be attributed to the mixed glass former effect in proton conducting glass.