Electrical Resistivity and Stoichiometry of CaxC60 and SrxC60 Films

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Science  04 Dec 1992:
Vol. 258, Issue 5088, pp. 1636-1638
DOI: 10.1126/science.258.5088.1636


The temperature- and concentration-dependent resistivities of annealed CaxC60 and SrxC60 films were measured near room temperature. Resistivity minima were observed at x = 2 and 5. The resistivities of these films were ρmin ∼1 ohm-centimeter for x = 2 and ρmin ∼10–2 ohm-centimeter for x = 5. This latter value is comparable to the resistivities found in similar experiments on K3C60 films. There is a maximum in the resistivity between x = 2 and 3, and another at x ∼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 Ca5C60 are associated with the population of bands derived from the t1g level of C6O.