Electronic properties of C-60 single crystals doped with lithium by electrodiffusion

Diffusion of lithium cations in C-60 single crystals driven by electric fie ld has been detected and studied. A novel technique for fullerene crystal d oping based on injection of ions through a "superionic crystal/C-60 single crystal" heterojunction has been suggested. It has been found that lithium doping of C-60 single crystals brings about an ESR signal, and this signal as a function of time has been investigated. The electronic conductivity in LixC60 crystals has a nonmetallic nature. Reflection spectra measured in t he IR band have shown that the reflectivity due to free electrons gradually decreases with time, which correlates with the evolution of signals due to ESR and microwave conductivity. Lithium doping of crystals increases the o scillator strength of the T-1u(4) vibrational mode and shifts it to lower f requencies (from 1429 cm(-1) to 1413 cm(-1)), which indicates that one elec tron is present at the C-60 molecule, and this fact may be treated as evide nce that the LiC60 phase is generated in a C-60 crystal. (C) 1999 American Institute of Physics. [S1063-7761(99)01511- 5].