The Structure of Borophosphosilicate Pure Network Former Glasses Studied by Multinuclear NMR Spectroscopy

Abstract

New mixed network glasses along the composition line xB2O3–(30 – x)P2O5–70SiO2 have been prepared and characterized in terms of their chemical composition, viscosity, and characteristic temperatures. The physical properties have been correlated with structural information, obtained from Raman spectroscopy and advanced 11B, 29Si, and 31P single and double resonance solid state NMR studies. Both the macroscopic and structural properties show nonlinear changes as a function of composition, with maximal values of the viscometric glass transition temperature near 12–13 mol % B2O3. The structure of phosphorus-rich glasses is dominated by tetrahedral B(4) units linked to three to four phosphorus species and multiple phosphorus environments, including P(3) (branching phosphate) groups linked to silicon, and P(4) units forming B–O–P linkages as in boron phosphate, BPO4 (superscripts denote the number of bridging oxygen species). In the boron-rich region, the phosphorus species are exclusively present as P(4) group...