The shock compaction of nanocrystalline silicon (nc-Si) powder with an average crystallite size of 50 nm was carried out at pressures of 1-4 GPa with several initial packing densities. The bulk of the shock-compacted nc-Si powder is characterized by X-ray diffraction analysis (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The observed XRD and Raman peaks correspond to silicon with a diamond structure, which is the same structure as the starting powder. With increasing pressure, the crystallite size of the compacts increases at a shock pressure of 1.8 GPa. The Raman peak width decreases with increasing shock pressure and also depends on the nature of the sample surface. The Raman peak width from a lustrous surface, which is also subjected to SEM observation, is wider than that of a textured surface. The SEM observation reveals that the textured surface contains droplet structures. It is suggested that a shock-induced temperature rise occurs during shock compaction and results in the melting and coarsening of nc-Si grains and the formation of droplet structures.

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