Electrical resistivity and stoichiometry of K_xC₆₀, Rb_xC₆₀, and Cs_xC₆₀ films

Electrical resistance measurements as a function of stoichiometry have been carried out on K_xC₆₀, Rb_xC₆₀ and Cs_xC₆₀ thin films for 0<x<6. The annealed films show global resistance minima at K₃C₆₀, ρ{variant}_min=4×10^-3 Ω cm (60°C), Rb₃C₆₀, ρ{variant}_min=4 × 10^-3 Ω cm, and Cs₁C₆₀, ρ{variant}_min=7 × 10^-2 Ω cm. All of the annealed films show additional features in the vicinity of x=4, but the manifestation of the A₄C₆₀ phase (A=K, Rb, Cs), in transport studies is dependent on the metal and the annealing conditions. The A₆C₆₀ phase is apparent for all of the metals studied and shows a relatively high resistivity. The activation energies of the conduction process show well defined stationary points at K₃C₆₀ (not activated), Rb₃C₆₀ (not activated). Cs₁C₆₀ (minimum), Cs₄C₆₀ (maximum), with less distinct features between 4 < x < 6 in all cases.