Local Structure of xAl2O3· (1 −x)NaPO3 Glasses: An NMR and XPS Study

Abstract

A series of xAl2O3· (1 −x)NaPO3 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). 27AI 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 31P MAS NMR spectra are consistent with bonding between neighboring P and Al polyhedra. Quantitative changes in the oxygen bonding, determined from the O 1s 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.