ULTRASONIC INVESTIGATIONS OF C-60 C-70 COMPOUNDS

We report on ultrasonic investigations of the frequency dependent and temperature dependent sound velocity in C60/C70 compounds. Although th e wellknown phase transitions at about 260K and 155K are clearly seen in our experiments, concerning the absolute values of the sound veloci ty our results differ markedly from those found by means of low freque ncy vibrating reed techniques on C60 single crystals. Reasons for this unexpected behaviour are discussed briefly.