Compressibility of CO intercalated C60 crystals

We report the pressure dependence of the cubic lattice parameter of (CO)xC60 at different temperatures, as determined by X-ray powder diffraction. In the measured range of pressures from 0.2 to 2 GPa, the volume is found to depend linearly on the pressure. The extrapolated volume bulk modulus of the ordered phase at room temperature is found to be K0=−V dP/dV=31.5(5) GPa. The bulk modulus at T=150 K is found as K0=26.9(5) GPa. The greater stiffness at higher temperature is explained by the entropic contribution of the CO molecules to the bulk modulus.