1. Borosilicate Glass Structure Jonathan F. Stebbins, Stanford University, DMR 0904094 Professor Stebbins of Stanford University shows the effect of composition and temperature on the structure of borosilicate glasses, which have silicon and boron oxides as the main ingredients. Glasses like these are widely used in high-tech materials ranging from fiber composites to computer display screens. Their atomic-scale structures change a lot with composition and temperature, in ways that greatly affect their physical properties, but little is known about these changes. Stebbins and graduate, undergrad, and high-school students in his group use high-resolution nuclear magnetic resonance (NMR) spectroscopy to quantify such changes. NMR allows the different bonding configurations to be distinguished and measured. Researchers have recently shown for a series of typical glass compositions that higher temperature promotes the conversion of borons with four to three oxygen neighbors, plus the formation of a “non-bridging” oxygen (figure 1). Although long hypothesized, this is the first time that the details of this reaction have been so directly documented. New data also show dramatic effects of composition, as sodium, barium, calcium and lanthanum are interchanged, examining the structures around boron,sodium, silicon and aluminum and oxygen ions with NMR. BO3 + NBO BO4 Caption 1. -50510152025 ppm BO3 high T low T Na Ca Ba BO4

2. Borosilicate Glass Structure Jonathan F. Stebbins, Stanford University, DMR 0904094 Professor Stebbins of Stanford University shows the effect of composition and temperature on the structure of borosilicate glasses, which have silicon and boron oxides as the main ingredients. Glasses like these are widely used in high-tech materials ranging from fiber composites to computer display screens. Their atomic-scale structures change a lot with composition and temperature, in ways that greatly affect their physical properties, but little is known about these changes. Stebbins and graduate, undergrad, and high-school students in his group use high-resolution nuclear magnetic resonance (NMR) spectroscopy to quantify such changes. NMR allows the different bonding configurations to be distinguished and measured. They have recently shown for a series of typical glass compositions that higher temperature promotes the conversion of borons with four to three oxygen neighbors, plus the formation of a “non-bridging” oxygen (figure). Although long hypothesized, this is the first time that the details of this reaction have been so directly documented. New data also show dramatic effects of composition, as sodium, barium, calcium and lanthanum are interchanged, examining the structures around boron,sodium, silicon and aluminum and oxygen ions with NMR. BO3 + NBO BO4 (above) Sketch showing glass network changes with composition and temperature. (below) Boron-11 NMR spectra of aluminoborosilicate glasses with different “modifier” cations, and effect of temperature. -50510152025 ppm high T low T Na Ca Ba BO4 BO3