Abstract
Using an effective genetic algorithm, we uncover the structure of a metastable Al41Sm5 phase that supplements its family sharing similar short-range orders. The phase evolves upon heating an amorphous Al-9.7 at.% Sm ribbon, produced by melt-spinning. The dynamical phase selection is discussed with respect to the structural connections between the short-range packing motifs in the amorphous precursor and those observed in the selected phases. The phase elucidated here is one of several newly discovered large-unit-cell phases found to form during devitrification from the glass in this binary system, further illustrating the power and efficiency of our approach, the important role of structural hierarchy in phase selection, and the richness of the metastable phase landscape accessible from the glassy structure.
Highlights
Using an effective genetic algorithm, we uncover the structure of a metastable Al41Sm5 phase that supplements its family sharing similar short-range orders
The phase elucidated here is one of several newly discovered large-unit-cell phases found to form during devitrification from the glass in this binary system, further illustrating the power and efficiency of our approach, the important role of structural hierarchy in phase selection, and the richness of the metastable phase landscape accessible from the glassy structure
We have recently developed an approach to solve for undetermined complex crystal structures observed in far-from equilibrium transitions[8,9]
Summary
Using an effective genetic algorithm, we uncover the structure of a metastable Al41Sm5 phase that supplements its family sharing similar short-range orders. Al-Sm alloys, known as marginal glass formers, provide a prototypical model system where a rich collection of intermediate meta-stable crystalline phases can be accessed through path-dependent devitrification processing[1,2,3,4]. The target Al-rich system (glassy structures are attainable from 7 to 13 at.% Sm) has a different composition from the above compounds, and a new Sm-cenered ordering was found in the Al-10 at.% system[7] This Sm-centered SRO transcends liquid, glass and crystalline states. The approach integrates lattice and space group information from X-ray diffraction (XRD) analysis with a genetic algorithm (GA) structural search With this approach, we have successfully identified several previously unknown large unit-cell (LUC) structures, including the ε-Al60Sm11 phase[8] and the θ-Al5Sm phase (i.e. Al20Sm4 in ref.[9]). We report on the discovery and identification of a LUC (~90 atoms/cell) tetragonal structure, termed hereafter as η-Al41Sm5 in this work
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