Orientational Disorder of C60 in Li2CsC60
Ichiro Hirosawa 1,
Kosmas Prassides 2,
Junichiro Mizuki 1,
Katsumi Tanigaki 1,
Matthew Gevaert 2,
Alexandros Lappas 2, and
Jeremy K. Cockcroft 3
1 Fundamental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba 305, Japan
2 School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9QJ, UK.
3 Department of Crystallography, Birkbeck College, London WC1E 7HX, UK.
The x-ray diffraction of the nonsuperconducting ternary fulleride Li2CsC60 reveals at room temperature a face-centered-cubic (Fm3m) disordered structure that persists to a temperature of 13 Kelvin. The crystal structure is best modeled as containing quasispherical [radius of 3.556(4) angstroms] C603- ions, in sharp contrast to their orientational state in superconducting face-centered-cubic K3C60 (merohedral disorder) and primitive cubic Na2CsC60 (orientational order). The orientational disorder of the carbon atoms on the C603- sphere was analyzed with symmetry-adapted spherical-harmonic functions. Excess atomic density is evident in the <111> directions, indicating strong bonding Li+—C interactions, not encountered before in any of the superconducting alkali fullerides. The intercalate-carbon interactions and the orientational state of the fullerenes have evidently affected the superconducting pair-binding mechanism in this material.
Submitted on March 3, 1994
Accepted on April 4, 1994
