In situ observation of a phase transition in silicon carbide under shock compression using pulsed x-ray diffraction

Abstract

The behavior of silicon carbide, SiC, under shock compression is of interest due to its applications as a high-strength ceramic and for general understanding of shock-induced polymorphism. Here we used the Matter in Extreme Conditions beamline of the Linac Coherent Light Source to carry out a series of time-resolved pump-probe x-ray diffraction measurements on SiC laser-shocked as high as 206 GPa. Experiments on single crystals and polycrystals of different polytypes show a transformation from a low-pressure tetrahedral phase to the high-pressure rocksalt-type (B1) structure. We directly observe coexistence of the low-and high-pressure phases in a mixed-phase region and complete transformation to the B1 phase above 2 Mbar. The densities measured by x-ray diffraction are in agreement with both continuum gas-gun studies and a theoretical B1 Hugoniot derived from static-compression data. Time-resolved measurements during shock loading and release reveal a large hysteresis on unloading with the B1 phase retained to as low at 5 GPa. The sample eventually reverts to a mixture of polytypes of the low-pressure phase at late times. Our study demonstrates that x-ray diffraction is an effective means to characterize the time-dependent structural response of materials undergoing shock-induced phase transformations at megabar pressures.

Femtosecond X‐Ray Diffraction of Laser‐Shocked Forsterite (Mg2SiO4) to 122 GPa

“…Our results show a strong correlation between and the peak stress, which was also not observed in the gas‐gun experiments. A large increase in in high‐strain‐rate laser‐driven compression experiments has also been reported in other materials (Smith et al., 2011; Tracy et al., 2019). None of the measured wave profiles show evidence for any additional multiwave structure that could be associated with a crystalline phase transformation or amorphization.…”

Subnanosecond phase transition dynamics in laser-shocked iron

“…In addition, recent molecular dynamic simulations of iron suggest the formation of a face-centered cubic (fcc) form (-phase) by shock compression at ~40 GPa (30). Over the past decades, advances in extremely bright x-ray sources, like the x-ray free electron lasers (XFEL) provided previously unknown capabilities to explore not only the structural changes of compressed material but also the dynamics of these phase transitions with high temporal resolution (31,32). It is unexpected that iron has not been studied yet using any XFEL sources despite its paradigmatic importance and discrepancies in understanding its phase transition dynamics.…”

SiO2‐SiC Mixtures at High Pressures and Temperatures: Implications for Planetary Bodies Containing SiC

“…Recent work has explored the SiC system at high P‐T through the LHDAC (Kidokoro et al, ; Miozzi et al, ; Nisr et al, ) and through shock experiments (Tracy et al, ). While we observe indication of SiC decomposition in our present experiments, as well as in previous measurements (Daviau & Lee, ), other studies probing similar conditions do not report the appearance of diamond diffraction or other indications of SiC decomposition.…”

“…In all cases, SiC at pressures less than 60 GPa will decompose, assuming complete decomposition is the stable form of SiC at these conditions, meaning that the upper mantle of a SiC containing planet will contain the decomposition products Si and C, rather than SiC. A Si + C composition has not been considered for a carbon planet previously, although high pressure SiC has been explored in several previous planetary motivated studies (Kidokoro et al, ; Madhusudhan et al, ; Miozzi et al, ; Nisr et al, ; Tracy et al, ; Wilson & Militzer, ).…”