EXAFS study of local structure at the alkali ions in superconducting K{sub 2}RbC{sub 60}, K{sub 2}CsC{sub 60}, Rb{sub 2}CsC{sub 60}, and Rb{sub 3}C{sub 60}
- Fachbereich Physik, Universitaet-GH Paderborn, D-33095 Paderborn (Germany)
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin-Dahlem (Germany)
We have studied the local site assignment as well as the structural and dynamic properties of the alkali ions in superconducting K{sub 2}RbC{sub 60}, K{sub 2}CsC{sub 60}, Rb{sub 2}CsC{sub 60}, and Rb{sub 3}C{sub 60} compounds by x-ray absorption fine structure (EXAFS) measurements at the alkali ions K, Rb, and Cs in the temperature range 14{endash}300 K. In the ternary {ital A}{sub 2}{ital B}C{sub 60} systems a strong preferential site occupation is observed, where the smaller alkali ions ({ital A}) are placed in tetrahedral sites and the larger ones ({ital B}) in octahedral sites. This site ordering allows a separate structural analysis of tetrahedral and octahedral sites. A quantitative analysis of the tetrahedral site ({ital A}) dopants yields the neighbor distances {ital R}({ital A}-{ital C}), coordination numbers {ital N}{sub {ital C}} and second cumulants {sigma}{sup 2}. A similar analysis of the tetrahedral sites in Rb{sub 3}C{sub 60} was performed by creating difference spectra with the K{sub 2}RbC{sub 60} system. A multishell analysis of the octahedral sites ({ital B}) yields an off-center position of the {ital B} dopants. The off-center displacement scales with the size of the octahedral site and inversely with the ionic radius of the {ital B} dopant. A preferential displacement in the (1,1,1) direction is discussed in conjunction with possible carbon neighbor configurations at the octahedral sites. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 389336
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 18 Vol. 54; ISSN PRBMDO; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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