Germanium goes glassy

By applying a lot of pressure to a little germanium, C. Austen Angell of Arizona State University and an international team of collaborators have prepared the first monatomic metallic glass (Nature 2007, 448, 787). Think of glasses as frozen liquids—their constituent atoms are closely packed and randomly ordered. But since the material doesn't flow as a liquid does, it is, for all practical purposes, a solid. While a number of substances can be coaxed into a glassy state, making glasses from monatomic metals is challenging because the molten metal has a strong tendency to crystallize when cooled below its melting point. Angell and coworkers thwarted crystallization in germanium by applying 7.9 gigapascals of pressure to the molten metal during the cooling process. The pressure reduces the temperature at which the metal normally crystallizes. Atomic motion at the new crystallization temperature becomes sluggish, and the germanium retains the disorder of its liquid phase as it solidifies.