Ultrasonic Study of Monomeric Fullerite C60 under Pressure

The ultrasonic study of the elastic moduli of polycrystalline fullerite C-60 was carried out in the temperature range from liquid nitrogen to room temperature at pressures up to 1.4 GPa, including the regions of the orientational fcc-to-sc and glass transitions. The temperature dependencies of the elastic moduli at ambient pressure are in good agreement with previous studies. For the first time the pressure dependencies of the shear modulus and Poisson's ratio were determined. Particularly, the Poisson's ratio was found to increase from approximate to 0.3 at ambient pressures to approximate to 0.38 at p = 1 GPa. The observed high values of the Poisson's ratio, as well as the high values of pressure derivatives of the bulk modulus approximate to 23-25 are discussed in terms of the central m-n power potential and contribution of the non-central intermolecular forces due to intramolecular deformations.