C-60 UNDER PRESSURE - BULK MODULUS AND EQUATION OF STATE

C-60 has been investigated under pressure up to 13 GPa using angular dispersive X-ray scattering and a diamond anvil cell. The resolution of the experimental setup allows to examine the volume decrease dV/dp under pressure even for pressures of a tenth of a GPa. The obtained data of numerous experimental runs result in a bulk modulus of 13.4 GPa, which is much smaller than the value reported by Duclos et al. [1]. At 170 K and 70 K a bulk modulus of 14.2 GPa and 14.7 GPa was obtained, respectively. The pressure induced fee-sc transition at 300 K was clearly visible at approx. 0.3 GPa with a jump in the lattice parameter of 0.05 Angstrom. With increasing pressure we found an extreme change in dV/dp, which disables the usage of common equations of state (EOS), like the Murnaghan [2] or Birch [3] equation. Considering the smalt compressibility of the fullerene molecules we suggest a modified EOS to describe the experimental data.