Fullerene glasses

We present the phase diagram of (C-60)(1-x)(C-70)(x) alloys, obtained from low frequency (1Hz) elastic and thermal expansion measurements. Whereas the rmal expansion measurements show only a fcc to sc phase transition in C-60- rich and a hcp to a distorted hcp phase transition in C-70-rich samples, lo w-frequency (1Hz) elastic compliance measurements show an additional dynami c anomaly for all the samples (except for the pure C-70) due to freezing of the molecular motion. This anomaly is centered around T-g approximate to 1 20 K for the pure C-60 and rises with rising concentration of C-70, reachin g T-g approximate to 150 K for mixtures with 95 mol% C-70 For C-70-rich sam ples with more than 10 mol% C-60 no orientational phase transition was foun d. The phase diagram can be described in terms of the orientational glass m odel.