X-Ray Diffraction of Ramp-Compressed Silicon to 390GPa.

Abstract

Silicon (Si) exhibits a rich collection of phase transitions under ambient-temperature isothermal and shock compression. This report describes insitu diffraction measurements of ramp-compressed Si between 40 and 389GPa. Angle-dispersive x-ray scattering reveals that Si assumes an hexagonal close-packed (hcp) structure between 40 and 93GPa and, at higher pressure, a face-centered cubic structure that persists to at least 389GPa, the highest pressure for which the crystal structure of Si has been investigated. The range of hcp stability extends to higher pressures and temperatures than predicted by theory.