TEMPERATURE AND CONCENTRATION-DEPENDENT CONDUCTIVITY OF POTASSIUM-DOPED C-60 FILMS IN RELATION TO THE PHASE-DIAGRAM

Conductivity measurements on potassium doped thin films of C-60 follow ing various preparation procedures are reported. In the resistivity as function of x we report a sharp local maximum at x = 4 and a local mi nimum near x = 5 in addition to that commonly found near x = 3. These effects are only seen in films prepared with ''backdoping''. For the x = 1 films we find a non-metallic quenched mestastable phase below 150 degrees C that can be annealed at 125 degrees C to a stable phase. Th e relevance of preparation methods and thermal history of the films fo r the existence of different phases is discussed.