Author(s): Krzysztof Kniaz, John E. Fischer, Andrew McGhie,
Louis A. Girifalco, Robert Strongin and Amos Smith III
Title: Fullerene Alloys
Source: Solid State Communications, v 96, p 739, 1995
Abstract: The results of differential scanning calorimetry (DSC)
and powder X-ray diffraction (XRD) on C60(x) - C70(1-x)
fullerene alloys are presented.
Samples have been prepared by solubilizing weighed amounts of
C60 and C70 in toluene and then evaporating the solvent, and
by subliming C60 - C70 powders under dynamic
vacuum. Dilute alloys prepared from toluene solution undergo
the orientational transition at lower temperatures than
pure C60 and C70, the depression of
the transition temperature (measured by the DSC)
depending on the alloy fraction.
These samples also exhibit a
large miscibility gap for x bigger than 0.04
and less than 0.95.
In contrast, alloys prepared by sublimation are
miscible in all
proportions, at least in the high-temperature fcc phase.
The experimental solubilities are compared with the
calculated binary phase diagram, in which
are treated by the Girifalco potential.
In the studied model C60-C70
alloy is treated essentially as a material made up of
huge "inert gas" molecules, interacting via Van der Waals
potential. Although the internal energy of mixing
for the system is positive ie fullerene alloy is not
energetically stable with respect to pristine components,
huge negative entropy of mixing makes the system stable.