New high-pressure phase of Si

Abstract

Angle-dispersive powder-diffraction techniques utilizing an image-plate area detector have been used to reexamine the high-pressure behavior of silicon to \ensuremath{\sim}18 GPa. We have observed a new intermediate body-centered orthorhombic structure between the well-known Si II (\ensuremath{\beta}-tin) and Si V (simple-hexagonal) structures. The existence of such a phase has been considered previously in energy calculations, and may pertain to the observed pressure dependence of the superconducting transition temperature of Si in the 13--18 GPa range.