EPR EVIDENCE OF THE LOW-TEMPERATURE PHASE-TRANSITION IN C-60

A standard EPR technique has been applied to perform temperature studi es of polycrystalline samples of C-60 fullerene. A comparison of the t hree main parameters of EPR spectra obtained for a C-60 sample before and after (solvent free) purification has been made in temperatures fr om 4 to 300 K. When compared to the spectrum of the as-obtained (crude ) sample the spectrum of the purified sample revealed considerable cha nges i.e. an increase in the EPR signal intensity and evidence of a ph ase transition at about 90 K. This transition is proved to be related to the two processes: freezing of the orientational motion of C-60 mol ecules and redistribution of the positive and negative charge observed as paramagnetic centres localized on C-60 molecules.