0

0.1

0.2

0.3

0.4

0.5

800 1200 1600 2000T, K

NBO

BO4

Pressure effects on borosilicate glass structureJonathan F. Stebbins, Stanford University, DMR 0404972

Oxide glasses rich in silicon, boron, and aluminum are widely used in high-tech materials from fiber composites to liquid-crystal computer display screens. Their atomic-scale structures must change a lot with temperature, in ways that affect their physical properties greatly, but little is known about these changes.

We are using high-resolution Nuclear Magnetic Resonance (NMR) spectroscopy to detect and quantify such changes. We have recently shown for a series of typical glass compositions that higher temperature promotes the conversion of borons with 4 oxygen neighbors to borons with 3 oxygen neighbors, plus the formation of a “non-bridging” oxygen. Although long hypothesized, this is the first time that the details of this reaction have been so directly documented. A simple thermodynamic model predicts data accurately.

30 20 10 0 -10 ppm

high T

low TBO3 + NBO

BO4

BO3 BO4

high-field,11B NMR spectra of sodium aluminoborosilicate glass

NMR data on boron coordination (BO4) and non-bridging oxygen (NBO) vs. model prediction

Pressure effects on borosilicate glass structureJonathan F. Stebbins, Stanford University, DMR 0404972

Oxide glasses rich in silicon, boron, and aluminum are widely used in high-tech materials from fiber composites to liquid-crystal computer display screens. When glass bends or breaks, parts of it can experience very high pressures. The atomic-scale structures must change a lot with pressure, but little is known about these changes.

We are using high-resolution Nuclear Magnetic Resonance (NMR) spectroscopy to detect and quantify such changes. In a recent collaboration with European colleagues, we have for the first time accurately measured such changes in a typical multicomponent glass subjected to “modest” pressure of 5000 atmospheres. The number of oxygen atoms increases around each Al and B atom at higher pressure, causing fundamental changes in glass properties.

low P

high P

BO3 + NBO

BO4 BO3

BO4

high-field,11B NMR spectra of aluminoborosilicate fiber glass

20 10 0 ppm

27Al NMR spectra 100 60 20 ppm

AlO5 AlO6

low P

high P

Structure and properties of oxide glasses: career development for the high-tech materials industry

Jonathan F. Stebbins, Stanford University, DMR 0404972

Our program trains students with diverse backgrounds in the science of oxide glass structure and properties. Three recent examples include T.J. Kinczenski, who finished his Ph.D. in Spring of 2005 and has gone on to a career in the research lab of Corning, Inc.; Lin-Shu Du, who was supported in this program as a postdoc and who left in early 2006 for a research position at a chemical company developing amorphous materials for the electronics industry (as well as many other products); and Jingshi Wu, a talented young woman with a mineralogy background who is interested in high-tech oxide materials and who is currently working in our Ph.D. program.