Phase transitions of C$_{70}$ fullerite under step-like shock compression

Shock-induced phase transitions of C$_{70}$ fullerite were studied with use of recovery assemblies of planar geometry at pressures 8 to 52 GPa. Two types of starting material were investigated: polyphase [1] and monophase C$_{70}$ with hcp-structure. We have found that the results of shock-wave compression of fullerite C$_{70}$ with various initial phase compositions qualitatively coincide in all explored pressure range. Rhombohedral modification of C$_{70}$ completely disappears already at pressure 9 GPa. At the same time, crystalline modification of C$_{70}$ with hcp-structure in conditions of step-like shock-wave compression does not undergo phase changes down to 9 GPa and practically completely disappears from the recovered material only at 23.5 GPa. Shock-induced transformation of hcp into fcc structure was fixed at pressures in the range 9 to 23.5 GPa. Depth of this transformation is increasing with growth of shock pressure. In the specimens recovered from 23.5 GPa, the only crystalline phase of fullerite C$_{70}$ with fcc structure is observed (about 5 {\%}) and for the first time formation of a graphite-like carbon is fixed (about 95 {\%}). With growth of shock pressure up to 26 GPa and higher, destruction of C$_{70}$ molecules occurs. The work was supported by RFBR and RSSF. [1] V.V. Milyavskiy, T.I. Borodina, S.N. Sokolov, A.Z. Zhuk. Diamond and Rel. Mat. \textbf{14} (2005) 1924.