Lattice Instability during Solid-Solid Structural Transformations under a General Applied Stress Tensor: Example of Si I → Si II with Metallization
The 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 → Si II PT is described by a critical value of the phase-field’s modified transformation work, and the PT criterion has only two parameters given six independent stress elements. Our findings reveal novel, more practical synthesis routes for new or known high-pressure phases under predictable nonhydrostatic loading, where competition of instabilities can serve for phase selection rather than free energy minima used for equilibrium processing.
This article is published as Zarkevich, Nikolai A., Hao Chen, Valery I. Levitas, and Duane D. Johnson. "Lattice Instability during Solid-Solid Structural Transformations under a General Applied Stress Tensor: Example of Si I→ Si II with Metallization." Physical Review Letters 121, no. 16 (2018): 165701. DOI: 10.1103/PhysRevLett.121.165701. Posted with permission.