Linus Pauling Institute

Analysis of the interatomic distances in the superconducting substance K3C60 indicates that each of the K atoms in tetrahedral interstices between C60 spheres accepts three electrons from C60, thus becoming quadricovalent; its four bonds resonate among the 24 adjacent carbon atoms to give a strong framework in which the negative charges are localized on these K atoms. The electric current is carried by the motion of positive charges (holes) through the network of C60 spheres and the K atoms in octahedral holes. Superconductivity is favored by the localization of the negative charges on the tetrahedral K atoms and their noninvolvement in valence-bond resonance, decreasing the rate of mutual extinction of electrons and holes.