EPR OF FULLERENE IONS AND SUPERCONDUCTIVITY IN K-FULLERIDES AT LOW DOPING LEVELS

Early stages of the potassium-doping process of C-60 were investigated with the EPR and MMMA techniques. Weak superconductivity of the (K C-60) mixture was found without heating or annealing the mixture. Upon heating two well-separated C-60(-1) and C-60(3-) EPR signals were fou nd. Two superconducting phases with T-c((1)) = (21 +/- 0.5) K and T-c( (2)),(18.5 +/- 0.5) K were also distinctly separated by increase of th e external magnetic field. To explain the appearance of the supercondu cting phase with T-c((1)) which is 2.5 K larger compared to the standa rd T-c((2)) of K3C60, a model has been developed.