Hugoniot of C₆₀ fullerite and sound velocity in shock-compressed fullerite were experimentally studied at the pressures range from 0.3 to 48 GPa.

In our experiments we used polycrystalline C₆₀ samples with a density 1.64 g/cc. The samples were loaded by impact of metal plates accelerated by gas gun (projectile velocities up to 0.53 km/s) or by preliminary calibrated explosive projectile systems (projectile velocities up to 5.3 km/s). The continuous monitoring of rear surface velocity of the samples was performed using laser interferometer VISAR through PMMA (low-pressure region) or water (high-pressure region) windows. To determine velocities of impactors and (or) shock velocities, contact gages or piezoelectric gages were used.

The Hugoniot of fullerite has a set of peculiarities, which are connected with a series of polymorphic phase transitions. For C₆₀ fullerite a transformation to a dense carbon phase is observed with a transition onset pressure 15 GPa, the stability limit of the fullerite structure under single-step shock compression. The two-wave structure of the transition is overdriven to a single wave above 33 GPa.

Previous to this work, behavior of fullerite under shock-wave compression was experimentally studied only with the use of recovery assemblies of various configurations (see, for example, review [1] for details). Our experimental results give new information about shock-induced phase transitions of C₆₀ fullerite and may be used as a basis for construction of the wide-range equation of state.

We thank L.G. Khvostantsev and I.V. Ustinov (IHPP RAS) for preparation of the samples. The work was supported by Russian Academy of Sciences and RFBR.

[1] V.V. Milyavskiy, A.Z. Zhuk, K.V. Khishchenko, Defect and Diffusion Forum 208-209 (2002) 161.

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