Local Structure Of Sodium Aluminum Metaphosphate Glasses

High-resolution solid-state 31P, 27Al, and 23Na nuclear magnetic resonance (NMR), Raman spectroscopy, differential scanning calorimetry, and density measurements were used to characterise the local structure of the glasses (1-x)(NaPO3)3.xAl(PO3)3. A systematic increase in density, glass transition temperature (Tg), 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 behaviour of Tg as a function of x was clearly detected. Also, changes of behaviour in the 23Na NMR line shape and in the Raman brand of the PO2 symmetric vibration are detected for concentrations higher than x = 0.17.