INTERNAL-FRICTION AND SOUND-WAVE VELOCITIES IN PURE C-60 FULLERITE

The temperature dependence of the attenuation and sound wave velocity of compacted pure C-60 fullerite is measured in the temperature interv al from 100 to 300 K at a frequency of about 5 MHz. Two internal frict ion peaks are observed at 250 and 215 K. The conclusion is made that t he internal friction peak at 250 K is connected with the structural ph ase transition and the peak at 215 K is due to the relaxation by reori entation of C-60 molecules in the stress field of ultrasonic waves. Th e magnitudes of the elastic moduli of C-60 fullerite are determined by sound velocity measurements. The results are compared with theoretica l estimations of the elastic moduli and experimental data of other aut hors.