实体相变过程中的机制

Two solids made of the same elements but with different geometric arrangements of the atoms, or crystal phases, can produce materials with different properties. Coal and diamond offer a spectacular example of this effect. While it is well known that one crystal phase can transform into another under the right circumstances, the mechanisms² that facilitate solid-to-solid transitions are still not well understood. Atoms can rearrange themselves to transform from a "parent" phase into a "daughter" phase by two major routes, but it is difficult to predict which route a material will take or why it took one route versus³ the other.   To this end, researchers from the Hong Kong University of Science and Technology, the University of Pennsylvania, Soochow University in Suzhou, China, and Solvay, have studied colloidal⁴ solid-solid transitions with single-particle resolution, and they have discovered a surprising mechanism¹ that facilitates one of these routes. They found that some crystals have an easier time of making the solid-solid transition if they take it in two steps.   Surprisingly, the first step of the process involves the parent phase producing droplets⁵ of liquid. The liquid droplets then evolve into the daughter phase.   The observations provide new insight for all sorts of solid-solid phase transformations⁶, and have potential implications for development and manufacture of alloys⁷, as well as natural processes that occur deep within Earth's mantle⁸.   The research team was led by graduate student Yi Peng and associate professor of physics Yilong Han, both of the Hong Kong University of Science and Technology, as well as Arjun Yodh, director of the Laboratory for Research on the Structure of Matter and professor in the Department of Physics and Astronomy in Penn's School of Arts & Sciences.   It was published in Nature Materials.