To the casual observer, the tiny crystal of gallium visible in the adjacent figure might seem remarkable primarily for its scale, just 40 nm—roughly 100 atoms—in diameter. But for the University of Western Australia’s Alexandra Suvorova, who took the transmission electron microscope (TEM) image, the bigger surprise was that the speck of frozen Ga was there at all. According to the metal’s phase diagram, the observed crystalline structure—a hexagonally packed arrangement known as the γ phase—occurs only at temperatures below 236 K, far cooler than the ambient temperature at which the image was taken.
Moreover, the diminutive lump of solid is enveloped in a shell of molten Ga, which seems to fly in the face of conventional rules of thermodynamics. Those rules stipulate that at a fixed pressure, a pure substance’s liquid and solid phases can coexist at precisely one temperature, the melting point. For Ga at atmospheric pressure, that...
