Sodium Ion Conductivity in Mixed Former Na2O-P2O5-GeO2 and Na2O-B2O3-P2O5-GeO2 Glasses

In this study, a mixed glass network effect (MGFE) is verified in two sodium ion conducting glass series: 40Na(2)O-(60 - x)P2O5-xGeO(2) and 40Na(2)O-10B(2)O(3)-(50 - x)P2O5-xGeO(2), x = 0-30 mol %. Network former substitution results in the significant electrical conductivity enhancement for both systems. This behavior is explained by the increased mobility of the Na+ ions, due to the depolymerization of the (boro)phosphate network and the emergence of easily conductive pathways after germanate incorporation and formation of various mixed Ge/P (Ge/B/P) structural units. With the help of 1D/2D MAS NMR techniques, we are able to determine and quantify structural units that form a glass network but also to gain insight into local environment and linkages between these units, which is crucial for determining the sodium ion transport mechanism.