Successive phase transitions of tin under shock compression

Longitudinal and bulk sound velocities of tin in the shock pressure range from ∼25to∼80GPa were measured using a direct reverse-impact method. The bct to bcc phase transition along the Hugoniot was identified by the discontinuity of the longitudinal sound velocity against shock pressure. The incipient melting on the Hugoniot was also revealed by the transition from longitudinal to bulk sound velocity. The shock pressure for bct-bcc phase transition and incipient melting were constrained to be ∼35 and ∼45GPa, respectively. It is inferred that the bcc phase possesses higher shear modulus than the bct phase.