Low Temperature Thermal Expansion of Cubic Fullerene C60

The anisotropy in the low temperature thermal expansion of C60 is analyzed theoretically. The generalized Grneisen parameters (Gps) of the elastic waves propagating in different directions in C60 are calculated using the second-order elastic constants and the first-order pressure derivatives of the second-order elastic constants. The expressions of effective second-order elastic constants are used to evaluate the six third-order elastic constants of the C60 system. The third-order elastic constants of C60 thus obtained are negative. The values of generalized Grneisen parameters are positive. The Brugger gamma is calculated and the low-temperature limit of Grneisen gamma is determined using the procedure of Menon and Ramji Rao. The value of low-temperature limit of Grneisen gamma is positive. There fore we expect volume expansion to be positive to absolute zero for C60 system. The anisotropy of thermal expansion along the three axis of crystal is less.