X-Ray Diffaction Evidence for Nonstoichiometric Rubidium-C60 Intercalation Compounds

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Science  25 Oct 1991:
Vol. 254, Issue 5031, pp. 545-548
DOI: 10.1126/science.254.5031.545


Powder x-ray diffraction at 300 K on equilibrated samples of several nominal compositions χ in RbχC60 is reported. In addition to the face-centered cubic (fcc) (χ = 3, superconducting), body-centered tetragonal (χ = 4), and body-centered cubic (bcc) (χ = 6) stoichiometric phases, direct evidence for a dilute fcc doped phase, 0 x c ≤ 1, and for a substoichiometric bcc phase, χ ∼ 5, is presented. In contrast, χ = 3 and χ = 4 appear to be line phases with nearly zero solubility of Rb vacancies and interstitials at 300 K. These results are summarized in a provisional binary phase diagram.