Local Structure of Sodium Aluminum Metaphosphate Glasses

High‐resolution solid‐state 31 P, 27 Al, and 23 Na nuclear magnetic resonance (NMR), Raman spectroscopy, differential scanning calorimetry, and density measurements were used to characterize the local structure of the glasses (1− x )(NaPO 3 ) 3 · x Al(PO 3 ) 3 . A systematic increase in density, glass transition temperature ( T g ), and frequencies of P–O stretching vibrations for terminal nonbridging oxygens (NBOs) was observed as the Al content was increased. A change of slope in the behavior of T g as a function of x was clearly detected around x = 0.25 ± 0.03. Also, changes of behavior in the 23 Na NMR line shape and in the Raman band of the PO 2 symmetric vibration are detected for concentrations higher than x = 0.17. According to these facts, a reorganization of the network affecting the degree of connectivity between phosphate chains is proposed to explain the observed behaviors of T g and P–NBO vibrations in these glasses.