On a Possible Melting Curve of C60 Fullerite

TL;DR

This paper estimates the melting curve of C60 fullerite at high temperatures and pressures using thermodynamic models and the Girifalco potential, providing insights into its melting behavior and decomposition temperature.

Contribution

It introduces a method to estimate the melting curve of C60 fullerite considering lattice anharmonicity and validates the approach with solid argon data.

Findings

Melting curve Tm(P) estimated up to 15 kbar and 4000 K.

Lattice anharmonicity significantly affects high-temperature behavior.

Melting point at normal pressure around 1500 K.

Abstract

We study the thermodynamic properties of the high-temperature modification of fullerites on the basis of the Girifalco intermolecular potential. In the present work, using Lindemann's melting criterion, we estimate a possible melting curve Tm(P) of C60 fullerite. To take into account the lattice anharmonicity, which has a strong effect at T > 700 K, we use the correlative method of unsymmetrized self-consistent field. To check this approach, first we have applied it to solid Ar. In the range between its triple point Tt = 83.807 K and 260 K we obtained the mean square relative deviation from experimental data of about 0.7%. The melting curve for C60 fullerite has been calculated from the melting point at normal pressure estimated at 1500 K up to 15 kbar, which corresponds to Tm = 4000 K, i.e. to the temperature estimated by Kim and Tom\'anek [Phys. Rev. Lett. 72, 2418 (1994)] as that of the decomposition of the C60 molecule itself.