Ultrasonic investigations of C60C70-compounds

Abstract We report on ultrasonic investigations of the frequency dependent and temperature dependent sound velocity in C 60 /C 70 compounds. Although the wellknown phase transitions at about 260K and 155K are clearly seen in our experiments, concerning the absolute values of the sound velocity our results differ markedly from those found by means of low frequency vibrating reed techniques on C 60 single crystals. Reasons for this unexpected behaviour are discussed briefly.