On thermoelastic phenomena around the orientational ordering transition in crystalline C 60

Abstract

The thermal expansion coefficient and isothermal compressibility in solid C 60 around the orientational phase transition are considered within the Landau theory of phase transitions. It is shown that the related anomalies originate from the order parameter evolution in the low-symmetry phase through a coupling with the homogeneous elastic strain. Relative values of the Landau theory parameters have been calculated from reported thermoelastic data. A wide temperature range of possible coexistence of the FCC phase with the SC one has been found from 260 K down to the critical temperature 160 K of the instability of the high-symmetry phase. The relevance of fluctuations is analyzed and the applicability of the Landau theory to ordering transition in fullerenes is discussed.