Electrical Resistivity and Stoichiometry of CaxC60 and SrxC60 Films

The temperature- and concentration-dependent resistivities of annealed CaxC(60) and SrxC(60) films were measured near room temperature. Resistivity minima were observed at x = 2 and 5. The resistivities of these films were rho(min) approximately 1 ohm-centimeter for x = 2 and rho(min) approximately 10(-2) ohm-centimeter for x = 5. This latter value is comparable to the resistivities found in similar experiments on K(3)C(60) films. There is a maximum in the resistivity between x = 2 and 3, and another at x approximately 7. The conductivity is activated over the whole range of compositions, and the activation energy scales with the logarithm of the resistivity. The results suggest that the conductivity and superconductivity observed in Ca(5)C(60) are associated with the population of bands derived from the t(1g) level of C(6O).