Affiliation:
1. Department of Chemistry University of Manitoba Winnipeg Manitoba Canada
2. Department of Chemistry University of Alberta Edmonton Alberta Canada
Abstract
AbstractInvestigations on binary lead‐bearing glass systems have shown that Pb2+ functions as a charge compensator at low concentrations and can participate in network formation at higher loadings. We use multinuclear magnetic resonance spectroscopy to investigate the mechanism underlying this dual‐role nature of Pb2+ in ternary lead‐borate glasses containing aluminum or gallium. 207Pb nuclear magnetic resonance (NMR) spectra—in conjunction with charge‐balance calculations, bond‐valence principles, and precedents from crystalline lead‐borates—are interpreted in terms of high‐ and low‐coordinate Pb2+ species, representing charge‐compensating “network modifier” sites and covalently‐bound “network forming” sites, respectively. Both high‐field 27Al and 71Ga magic‐angle spinning NMR spectra indicate the presence of substantial fractions of four, five, and six‐fold coordinated Al/Ga, reinforcing the isostructural nature of these elements. However, systematic differences in the boron speciation in Al‐ and Ga‐bearing glasses reveal that their size difference has a measurable effect on the short‐range structure in these glasses.