Compositional and Temperature Controls on Structural Order and Properties of Technological Oxide Glasses: NMR Studies and Thermodynamic Analyses

Stanford University, Stanford CA

Investigators

Abstract

The overall goal of this project is to better understand and predict the effects of composition and temperature on the physical and chemical properties of oxide glasses and glass-forming liquids, especially those containing major amounts of boron oxide. Such materials have widespread use in technology and are also fascinating examples of complex, partially disordered network systems. The primary experimental approach will be to use solid-state Nuclear Magnetic Resonance (NMR) to quantitatively determine the short- to intermediate-range structure. Advanced methods to enhance spectroscopic resolution, such as multiple quantum 11B, 17O and 27Al NMR and the use of the very high field spectrometers (e.g. 14.1 and 18.8 Tesla), will be applied. Crystalline model compounds will be synthesized as needed to help correlate local atomic structure with experimental observables, and to test the quantitation of spectra of glasses. Temperature effects on the structure of precursor liquids will be explored by studying samples of glass cooled at a wide range of rates, facilitated by a specially developed rapid quench apparatus. Structure-based thermodynamic models will be developed in order to link spectroscopic results to critical properties such as configurational entropy, free energy, and thermal expansivity. Other oxide glass systems will be explored as well, such as oxyfluorides, oxychlorides, aluminophosphates, and germanosilicates. Oxide glasses are used in many critical technologies, from the relatively mundane (e.g. fiber glass) to the high-tech (e.g. flat screen computer displays and optical data processing). Many of these glasses contain boron oxide to help tailor their properties to the application. Improvements in this technology are still often made by expensive, trial-and-error methods. Nuclear Magnetic Resonance (NMR) is one of the few available methods that can quantitatively determine the atomic-scale structure of these complex but vital materials, which in turn is essential to formulating accurate, predictive models of how variations in composition and temperature can be used to optimize their properties and invent new applications.