ELECTRON-SPIN-RESONANCE STUDY OF THE DIMER STATE OF KC60 AND ITS TRANSFORMATIONS

Recent x-ray results show that quenching the high-temperature fcc (rocksalt) phase of KC60 below 280 K produces a metastable orthorhombic structure in which the molecules exist as dimer pairs. Using electron-spin resonance, we find that this state is nonmagnetic and describe evidence for σ bonding. Upon heating, the dimer structure transforms first to the fcc phase at 280 K. The fcc phase is unstable at 300 K and transforms to the polymeric state at 340 K rather than undergoing equilibrium phase separation. We suggest that the transformation from dimer to fcc is driven by the onset of molecular orientational disorder. © 1995 The American Physical Society.