期刊
PHYSICAL REVIEW MATERIALS
卷 1, 期 5, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevMaterials.1.055601
关键词
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资金
- US Department of Energy, Basic Energy Sciences, Materials Science Division and Engineering [DE-AC02-07CH11358]
- Argonne National Laboratory [DE-AC02-06CH11357]
- China Scholarship Council [201406340015]
- National Natural Science Foundation of China [11574289]
- USTC Qian-Ren B (1000-Talents Program B) fund
Investigating the unknown structure of the complex cubic phase, previously observed to crystallize from melt-spun amorphous Al-10 at.% Sm alloy, we determine the structure in full site-occupancy detail, highlighting several critical structural features that govern the far-from-equilibrium phase selection pathway. Using an efficient genetic algorithm combining molecular dynamics, density functional theory, and x-ray diffraction, the structure is clearly identified as body-centered cubic Im (3) over barm (No. 229) with similar to 140 atoms per cubic unit cell and a lattice parameter of 1.4 nm. The complex structure is further refined to elucidate the detailed site occupancy, revealing full Sm occupancy on 6b sites and split Sm/Al occupancy on 16f sites. Based on the refined site occupancy associated with the experimentally observed phase, we term this phase epsilon-Al60Sm11(bcc), corresponding to the limiting situation when all 16f sites are occupied by Sm. However, it should be recognized that the range of solubility enabled by split occupancy at Sm sites is an important feature in phase selection under experimental conditions, permitting an avenue for transition with little or no chemical partitioning. Our analysis shows that the epsilon-Al60Sm11(bcc) exhibits a 3-6-6-1 first-shell packing around Sm centers on 16f sites, the same dominant motif exhibited by the undercooled liquid. The coincident motif supports the notion that liquid/glass ordering at high undercooling may give rise to topological invariants between the noncrystalline and crystalline states that provide kinetic pathways tometastable phases that are not accessible during near-equilibrium processing.
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