Deformation, lattice instability, and metallization during solidsolid structural transformations under general applied stress tensor: example of Si I > Si II
Abstract
Density functional theory (DFT) was employed to study the stressstrain behavior, elastic instabilities, and metallization during a solidsolid phase transformation (PT) between semiconducting Si I (cubic A4) and metallic Si II (tetragonal A5 structure) when subjected to a general stress tensor. With normal stresses ($\sigma_1$, $\sigma_2$, $\sigma_3$) acting along $\left<110 \right>$, $\left<1\bar{1}0 \right>$, and $\left<001\right>$, respectively, dictating the simulation cell, we determine combinations of 6 independent stresses that drive a lattice instability for the Si I$\rightarrow$Si II PT, and a semiconductormetal electronic transition. Metallization precedes the structural PT, hence, a stressed Si I can be a metal. Surprisingly, a stressfree Si II is metastable in DFT. Notably, the PT for hydrostatic pressures is at 75.81 GPa, while under uniaxial stress it is 11.03 GPa (or 3.68 GPa mean pressure). Our key result: The Si I > Si II PT is described by a critical value of the modified transformation work, as found with a phasefield method, and the PT criterion has only two parameters for a general applied stress. More generally, our findings are crucial for revealing novel (and more economic) material synthesis routes for new or known highpressure phases under controlled and predictable nonhydrostatic loading and plastic deformation.
 Publication:

arXiv eprints
 Pub Date:
 May 2018
 arXiv:
 arXiv:1806.00055
 Bibcode:
 2018arXiv180600055Z
 Keywords:

 Condensed Matter  Materials Science
 EPrint:
 10 pages, 11 figures