20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017;
St. Louis, Missouri
Session F7: Phase Transitons II
5:00 PM–6:30 PM,
Monday, July 10, 2017
Room: Regency Ballroom F
Chair: Jow-Lian Ding, Washington State University
Abstract ID: BAPS.2017.SHOCK.F7.1
Abstract: F7.00001 : Shock-induced phase transformations in silicon: continuum and x-ray diffraction measurements*
5:00 PM–5:30 PM
Preview Abstract
Abstract
Author:
Stefan Turneaure
(Washington State University)
Silicon under static compression undergoes a sequence of structural
transformations with increasing pressure [Mujica et al., Rev. Mod. Phys. 75,
863 (2003)]. Previous dynamic compression experiments on silicon using
different drivers and various diagnostics have not provided observations of
any high-pressure silicon crystal structures but have raised many questions.
For example, impact loading of millimeter scale thickness Si(100) samples
from 16-22 GPa results in the formation of 3 shock waves transmitted through
the material [Turneaure and Gupta, Appl. Phys. Lett. 91, 201913 (2007)]. The
first wave compresses the silicon elastically and at the HEL (9 GPa) the
stress deviators are large. Inelastic deformation occurs in the second wave,
but the mechanisms responsible for relaxation of the stress deviators are
not understood. Continuum and x-ray diffraction (XRD) measurements
demonstrate that the stress deviators remain nonzero between the HEL and the
phase transformation stress [Turneaure and Gupta, J. Appl. Phys. 111, 026101
(2012)]; the role of the stress deviators on the structural changes in
silicon is an open question. A large volume collapse occurs in the third
(phase transformation) wave with the peak state stress-density being
consistent with one of the high-pressure structures observed for statically
compressed silicon, but the structure in the peak state could not be
determined from earlier experiments. Using multi-frame powder XRD
measurements at the Dynamic Compression Sector the crystal structure of
polycrystalline and single crystal silicon shock compressed to 26 GPa (and
then partially released to 19 GPa) was directly examined [Turneaure and
Gupta, Phys. Rev. Lett. 117, 045502 (2016)]. Both polycrystalline and single
crystal silicon were found to transform to the simple hexagonal structure
under shock compression. An important finding was that shock compression of
single crystal silicon resulted in a highly textured simple hexagonal phase.
Comparison of diffraction simulations for textured simple hexagonal silicon
with the measured diffraction patterns revealed the orientation relations
between the ambient cubic diamond and simple hexagonal silicon structures.
The experimental approach and analysis procedures are general, and are being
used at the Dynamic Compression Sector to examine orientation relations
between low and high-pressure structures in other shocked single crystal and
textured materials.
*Work supported by DOE/NNSA. This work was carried out in collaboration with Y. M. Gupta.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2017.SHOCK.F7.1