Crystal Structure, Bonding, and Phase Transition of the Superconducting Na2 CsC60 Fulleride

    loading  Checking for direct PDF access through Ovid

Abstract

The crystal structure of superconducting Na2 CsC60 was studied by high-resolution powder neutron diffraction between 1.6 and 425 K. Contrary to the literature, the structure at low temperatures is primitive cubic (Pa overbar 3), isostructural with pristine C60. Anticlockwise rotation of the C60 units by 98 degrees about [111] allows simultaneous optimization of C60-C60 and alkalifulleride interactions. Optimal Naplus -C603 minus coordination is achieved with each sodium ion located above one hexagon face and three hexagon-hexagon fusions of neighboring fulleride ions (coordination number 12). Reduction of the C60 molecule lengthens the hexagon-hexagon fusions and shortens the pentagon-hexagon fusions (to approximate 1.43 angstroms). On heating, Na2 CsC60 undergoes a phase transition to a face-centered-cubic Fm overbar 3 m phase, best modeled as containing quasi-spherical C603 minus ions. The modified structure and intermolecular potential provide an additional dimension to the behavior of superconducting fullerides and should sensitively affect their electronic and conducting properties.

Related Topics

    loading  Loading Related Articles