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Lattice instability during solid-solid structural transformations under general applied stress tensor: example of Si I to Si II with metallization

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posted on 28.09.2018 by Nikolai Zarkevich, Hao Chen, Valery Levitas, Duane Johnson

Density functional theory was employed to study the stress-strain behavior and elastic instabilities during the solid-solid phase transformation (PT) when subjected to a general stress tensor, as exemplified for semiconducting Si I and metallic Si II, where metallization precedes the PT, so stressed Si I can be a metal. The hydrostatic PT occurs at 76 GPa, while under uniaxial loading it is 11 GPa (3.7 GPa mean pressure), 21 times lower. The Si I to Si II PT is described by a critical value of phase-field’s modified transformation work, and the PT criterion has only two parameters given 6 independent stress elements. Our findings reveal novel, more practical synthesis routes for new or known high-pressure phases under predictable non-hydrostatic loading, where competition of instabilities can serve for phase selection, rather than free energy minima used for equilibrium processing.

Funding

Nikolai A. Zarkevich and Duane D. Johnson are supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. NAZ completed this work support by DOE’s Advanced Manufacturing Office, Office of Energy Efficiency & Renewable Energy, through CaloriCool. Ames Laboratory is operated for DOE by Iowa State University under contract DE-AC02-07CH11358. Valery I. Levitas and Hao Chen are supported from NSF (CMMI-1536925 and DMR-1434613), ARO (W911NF- 17-1-0225), ONR (N00014-16-1-2079), and XSEDE (TG-MSS140033 and MSS170015).

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