Finding Order Amid the Chaos
Glass is often described as being like a liquid, with randomly arranged atoms. New insights are emerging that show some distinct levels of order within the structure of glasses. Our rapidly evolving understanding arises from new structural information made possible because of advanced light sources like the U.S. Department of Energy’s Advanced Photon Source. The new theory fits experimental data better than the widely accepted model based on icosahedral-like clusters. The new model shows many crystal-like polyhedra as well as clustering of polyhedra — features not seen in previous models. Similar clusters group together into nanometer sized regions. The structure emerges by linking short range effects determined from the forces acting on each atom, with medium range information from electron microscopy. After heating for long periods of time to encourage structural relaxation, glasses increasingly conform to the older model suggesting that this represents an ideal glass. Practical glasses that are not heated for so long have more complex structures. This has important implications for designing and manufacturing metallic glasses.
- J. Hwang, Z. H. Melgarejo, Y. E. Kalay, I. Kalay, M. J. Kramer, D. S. Stone, and P. M. Voyles. Nanoscale Structure and Structural Relaxation in Zr50Cu45Al5 Bulk Metallic Glass. Physical Review Letters, 2012, 108, 195505. DOI: 10.1103/PhysRevLett.108.195505