Reduction of Shear Strength and Phase-Transition in Shock-Loaded Silicon

Abstract

Shock wave profile measurements on Si were performed to 60 GPa. Three shock wave structures arising from dynamic yielding and structural transition were observed between 19 and 30 GPa. The Hugoniot elastic limit (HEL) is determined to be 8.4 GPa in the [100] direction and 5.6 GPa in the [110] and [111] directions. Unusually low shock velocities just above HEL, compared with the bulk sound velocity, are successfully analyzed by assuming complete loss of shear strength in the yield state. The phase transition pressure is determined to be 13.4±.2 GPa, which compares favorably with the semiconductor-metal transition observed at static pressures.