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NMR Non-Crystallography

The Nature of Glass remains anything but clear

Non-crystalline or glassy materials are ubiquitous in our society. From shards of naturally occurring obsidian glass used as simple tools and art objects in early human history to fiber optics used in high speed data communication or metallic glasses used for their superior strength and hardness, glasses today continue to play a diverse and vital role in many aspects of our daily lives. While the development of new materials and applications continues to be a highly active field, there remain a number of fundamentally significant and profound mysteries about the glassy state. While many theories abound there is still no universally accepted theory for the glassy state. Surprisingly, most theories are based on structural evidence from pair correlations. It has long been argued that higher-order or ``locally favored'' structures may exist in glasses, but there have been few experimental methods capable of measuring such structures in non-crystalline materials. Our lab has a strong focus on developing NMR methodologies for measuring and quantifying short- and medium-range structures in non-crystalline materials with unprecedented new levels of precision and sensitivity. Uncovering these higher order structures and their patterns of occurrence is essential for future models of the glassy state. These structural distributions measured are also needed for confirming thermodynamic models of oxide glasses and melts, models for ionic transport, and also for refining potentials in molecular dynamics simulations of structure and dynamics in glasses.

Over the last ten years, our research group has been developing two-dimensional solid-state nuclear magnetic resonance (NMR) methods and analyses for answering just this question. In our recent work , we've applied these and other advances to obtain, for the first time, quantitative measurements of the two-dimensional distribution of Si-O distances and Si-O-Si angles in the glass. This new advance opens the door for measuring previously inaccessible structural details in a variety of silicate based materials, and obtaining new insights into structure/property relationships.