中熵稀土合金中压力诱导的堆垛无序与长程Sm型有序的抑制
Pressure-Induced Stacking Disorder and Suppression of Long-Range Sm-type Order in Medium-Entropy Rare-Earth Alloys
AI总结：
该研究通过同步辐射X射线衍射发现，中熵稀土合金TbHoEr和TbHoDy在压力下跳过Sm型中间相，经堆垛无序的密堆积态转变，揭示中熵合金化可改变稀土材料的压力诱导堆垛路径。
AI中文摘要：
稀土中熵合金为研究化学无序如何改变密堆积4f镧系元素的压力诱导结构演化提供了平台。本研究利用金刚石对顶砧中的同步辐射X射线衍射，对TbHoEr和TbHoDy两种合金进行研究：两种合金均从环境条件下的六方密堆积（hcp）结构转变为双六方密堆积（dhcp）相，未观测到清晰的体相Sm型中间相；其中TbHoEr在压缩至70 GPa时进一步呈现出高压菱方hR24相。与组成的重镧系元素不同，两种合金均跳过了中间Sm型相。二维衍射图像还显示转变区域存在条纹状漫散射，表明沿密堆积方向存在堆垛无序和有限的堆垛相干性。这些观测结果表明，转变是通过堆垛无序的密堆积态而非有序的体相Sm型相进行的。研究提出，构型无序、局域晶格畸变、堆垛层错能以及转变动力学共同抑制了长程Sm型有序的形成，结果表明中熵合金化可从根本上改变极端条件下稀土材料的压力诱导堆垛路径。
英文摘要：
Rare-earth medium-entropy alloys provide a platform for investigating how chemical disorder modifies the well-established pressure-induced structural evolution of close-packed $4f$ lanthanides. Here, we study TbHoEr and TbHoDy using synchrotron X-ray diffraction in diamond anvil cells. Both alloys transform from the ambient hexagonal close-packed (hcp) structure to a double hexagonal close-packed (dhcp) phase, while no well-resolved bulk Sm-type intermediate phase is observed. For TbHoEr, compression to 70 GPa further reveals a high-pressure rhombohedral hR24 phase. Unlike the constituent heavy lanthanides, however, both alloys bypass the intermediate Sm-type phase. Two-dimensional diffraction images further reveal streak-like diffuse scattering in the transition region, indicating stacking disorder and limited stacking coherence along the close-packed direction. These observations indicate that the transformation proceeds through a stacking-disordered close-packed state rather than through a well-ordered bulk Sm-type phase. We propose that configurational disorder, local lattice distortion, stacking-fault energetics, and transformation kinetics collectively suppress the development of long-range Sm-type order. The results demonstrate that medium-entropy alloying can fundamentally modify pressure-induced stacking pathways in rare-earth materials under extreme conditions.
