Local structure of xAl2O3·(1 - ital x)NaPO3 glasses

A series of xAl2O3 circle (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). Al MAS NMR spectra reveal that: at low alumina contents (x < 0.125), 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