OXYGEN DIFFUSION IN C-60 FILMS

We have performed detailed resistivity measurements as a function of temperature in the range from 12 to 300 K on oxygen loaded C-60 films. We observe that two ordering phase transitions (i.e., T-0=260 K and T-g=90 K) are present in rho(T), which, in addition, strongly depends on the oxygen content. We find a decrease of both ordering temperatures with increasing oxygen concentrations. The mechanisms of oxygen diffusion are greatly enhanced in the ordered phase on heating. Finally, the transition to a glassy state at T-g is detected as a point of reversibility of the resistivity curve as a function of temperature.