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X-ray-diffraction data have been obtained on Si in a diamond anvil cell to pressures of 50 GPa. Crystallographic data are presented in phase I (cubic, diamond), II (tetragonal, -Sn), V (simple hexagonal), VII (hexagonal close-packed), and the metastable phase III body-centered-cubic (BC8) and on the coexistence of the phases. Comparison is made between these data and the predictions of ab initio calculations for these structures and their equations of state.
Hu et al. (Wed,) studied this question.