您目前的位置: 首页» 研究成果» 重要科研进展

Polymorphism in a high-entropy alloy

Polymorphism, which describes the occurrence of different lattice structures in a crystalline material, is a critical phenomenon in materials science and condensed matter physics. Recently, configuration disorder was compositionally engineered into single lattices, leading to the discovery of high-entropy alloys and high-entropy oxides. For these novel entropy-stabilized forms of crystalline matter with extremely high structural stability, is polymorphism still possible? Here, by employing in situ high-pressure synchrotron radiation X-ray diffraction, we reveal a polymorphic transition from fcc (face-centered-cubic)-to-hcp (hexagonal-close-packing) in the prototype CoCrFeMnNi high entropy alloy. The transition is irreversible, and our in situ high-temperature synchrotron radiation X-ray diffraction experiments at different pressures of the retained hcp HEA unambiguously reveal that the fcc phase was a stable polymorph at high temperatures, while the hcp structure is more thermodynamically favorable at lower temperatures. As the pressure is increased, the critical temperature for the hcp to fcc transformation also rises.