skip to main content

DOE PAGESDOE PAGES

This content will become publicly available on October 12, 2018

Title: Structural hierarchy as a key to complex phase selection in Al-Sm

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¯3m (No. 229) with ~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 ε–Al 60Sm 11(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 ε–Al 60Sm 11(bcc) exhibits a “3-6-6-1” first-shell packing around Sm centers on 16f sites, the same dominant motif exhibited bymore » the undercooled liquid. Here, 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 to metastable phases that are not accessible during near-equilibrium processing.« less
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [3] ;  [1] ;  [1] ;  [4] ;  [5]
  1. Ames Lab., Ames, IA (United States)
  2. Ames Lab., Ames, IA (United States); Univ. of Science and Technology of China, Anhui (China)
  3. Univ. of Science and Technology of China, Anhui (China)
  4. Ames Lab. and Iowa State Univ., Ames, IA (United States)
  5. Ames Lab. and Iowa State Univ., Ames, IA (United States); Univ. of Science and Technology of China, Anhui (China)
Publication Date:
Report Number(s):
IS-J-9483
Journal ID: ISSN 2475-9953; PRMHAR; TRN: US1703161
Grant/Contract Number:
AC02-07CH11358; AC02-06CH11357; 201406340015; 11574289
Type:
Accepted Manuscript
Journal Name:
Physical Review Materials
Additional Journal Information:
Journal Volume: 1; Journal Issue: 5; Journal ID: ISSN 2475-9953
Publisher:
American Physical Society (APS)
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1408051
Alternate Identifier(s):
OSTI ID: 1399170