Local Structure of x Al 2 O 3 · (1 − x )NaPO 3 Glasses: An NMR and XPS Study

A series of x Al 2 O 3 · (1 − x )NaPO 3 glasses (0 ≤ x ≤ 0.275) were prepared and characterized by magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and by X‐ray photoelectron spectroscopy (XPS). 27 AI MAS NMR spectra reveal that: at low alumina contents ( x < 0.125), Al is in dominantly octahedrally coordinated Al(OP) 6 structural environments; in glasses with x > 0.125, Al(OP) 4 environments are increasingly favored; and at x = 0.275, most Al is tetrahedrally coordinated. 5‐coordinated Al environments also appear to be present. Variations in the 31 P MAS NMR spectra are consistent with bonding between neighboring P and Al polyhedra. Quantitative changes in the oxygen bonding, determined from the O 1 s spectra obtained by XPS, also reflect these structural changes. The effects of alumina content on the relative concentration of nonbridging oxygen (PO − ) are quantitatively described by a simple structural model derived from the MAS NMR data. The thermal expansion coefficients and glass transition temperatures are shown to be sensitive to these structural changes.