Unveiling the Electronic Origin for Pressure-Induced Phase Transitions in High-Entropy Alloys

Understanding and controlling pressure-related structural transformations, which can be utilized to tune functional and mechanical properties of materials, is one of the most important research themes in materials science. However, the underlying mechanism governing pressure-driven phase transformations in high-entropy alloys (HEAs) remains poorly understood. By combining an in situ high-energy X-ray diffraction (XRD) technique and ab initio calculations, we reveal that the face-center-cubic (fcc) phase, rather than the hexagonal-close-packed (hcp) phase, is thermodynamically stable in the Mo_xCrFeCoNi HEA system under atmospheric conditions. However, a fcc to hcp transformation was identified under pressure, resulting from a pressure-induced electronic redistribution. Remarkably, the valence electron concentration has been further demonstrated as a critical factor for regulating this transformation, the reduction of which by Mo doping can encourage the hcp transformation. Our studies provide new insights into the physical processes underlying the allotropic transformation that enables customized alloy design of high-performance HEAs.