Shock-compressed silicon: Hugoniot and sound speed up to 2100 GPa

Abstract

High-pressure equation of state and isentropic sound speed data for fluid silicon to pressures of 2100 GPa (21 Mbar) are reported. Principal Hugoniot measurements were performed using impedance matching techniques with \ensuremath{\alpha}-quartz as the reference. Sound speeds were determined by time correlating imposed shock-velocity perturbations in both the sample (Si) and reference material (\ensuremath{\alpha}-quartz). A change in shock velocity versus particle velocity (${u}_{s}--{u}_{p}$) slope on the fluid silicon principal Hugoniot is observed at 200 GPa. Density functional theory based quantum molecular dynamics simulations suggest that both an increase in ionic coordination and a 50% increase in average ionization are coincident with this experimentally observed change in slope.