The Mixed-Network Former Effect in Phosphate Glasses: NMR and XPS Studies of the Connectivity Distribution in the Glass System (NaPO3)1−x(B2O3)x

Abstract

The structural organization of sodium borophosphate glasses with composition (NaPO3)1−x(B2O3)x (0.0 ≤ x ≤ 0.3) has been investigated by X-ray photoelectron spectroscopy (XPS), as well as single- and double-resonance 11B and 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. O-1s XPS data provides a quantitative distinction between B−O−B, B−O−P, and P−O−P linkages as well as nonbridging oxygen atoms. 11B and 31P MAS NMR data indicate that within the compositional region 0 ≤ x ≤ 0.20 the entire boron inventory is present in the form of anionic BO4− units, resulting in the repolymerization of an equivalent fraction of the phosphate units (conversion of anionic metaphosphate (P(2)) into neutral branching groups (P(3)) species. Both XPS as well as 31P{11B} and 11B{31P} rotational echo double resonance (REDOR) NMR results reveal strong interactions between the two network formers boron oxide and phosphorus oxide, resulting in the dominant formation of B−O−P linkages. In addition, the ...