Tin has complex phase diagram under high pressure, which makes it an important material for experimental and theoretical study of multiphase equation of state. In this study, we combined laser ramp compression with in-situ X-ray diffraction measurements to explore the solid crystal structure of tin under high pressure, and compressed tin up to 598 GPa. The temperature of ramp compression path was adjusted by initial shock compression prior to ramp compression. The crystal structure data obtained from the experiment are consistent with BCC structure in the range of 87 to 598 GPa. At 73 GPa (about 3000 K), the observed crystal structure deviates obviously from BCC structure and is consistent with BCO structure. This data point is close to the temperature and pressure range of shock melting of tin, which indicates that there may be a coexistent of BCO, BCC and liquid phase in the shock melting interval. The BCO structure has been excluded from the recent high pressure phase diagrams of tin based on first-principles calculations (D. A. Rehn, et al. 2020, G. Deffrennes, et al.2022). Combined with our experimental results, we suggest that BCO phase should be included in the multiphase equation of state model.

tin; phase diagram; high pressure