In-situ characterization of silicon deformation mechanism at high-pressure: comparison between static and dynamic compression

Silicon (Si) is an ideal model system to investigate the properties of planetary materials. The interpretation of experimental results can be simplified thanks to samples of remarkably high purity and low defect density, making precise characterization of Si deformation mechanism viable. Understanding Si behaviour at extreme conditions will help to interpret the response of high-strength and Si-bearing compounds, which are important planetary materials.

Despite an extended experimental effort, the complex behaviour of Si under high pressure is not yet fully understood. In particular, Si deformation under high strain rate (i.e. dynamic compression regime dε/dt∼10⁵-10⁹ s^-1) is still a matter of debate, as experimental proofs have been presented supporting both a lowering [1] and an increase [2] of the transition onsets compared to quasi-static loading. Here we present the characterization of Si phase transitions below 20 GPa investigated by in-situ x-ray diffraction during laser-driven shock-compression. Experiments were performed at the Matter in Extreme Conditions End Station at the Linac Coherent Light Source, SLAC, National Accelerator Laboratory.

Exploiting the ultra-fast (sub-picoseconds) temporal resolution, our study captured in-situ the microstructural evolution of shock-compressed single crystalline Si, focusing on the analysis of the transition mechanism and mosaicity evolution. Shock-compression experiments are also compared with quasi-hydrostatic ones performed in a multi-anvil apparatus (i.e. dε/dt∼10^-5 s^-1), thus providing further insight on the kinetics of these transitions.

[1] EE McBride et al., Phase transition lowering in dynamically compressed silicon, Nature Physics (2019)

[2] RF Smith et al., Orientation and rate dependence in high strain-rate compression of single-crystal silicon, Physical review B (2012)