Sluggishness in the phase transformation in solid C<SUB>70</SUB>

In an earlier paper [G. Ghosh, V.S. Sastry, C.S. Sundar, T.S. Radhakrishnan, Solid State Commun. 105 (1998) 247] we have reported that at low temperatures the ideal hcp (c/a~1.63) solid C70transforms to a monoclinic structure, in a single step. The transition is broadened over a temperature interval of about 100 K, for a cooling rate ~0.0033 K/min, indicating the coexistence of two phases in this temperature range. The width of broadening is cooling-rate dependent [G. Ghosh, V.S. Sastry, C.S. Sundar, S. Sengupta, T.S. Radhakrishnan, Phys. Rev. B 58 (1998) 14 094]. We have observed experimentally that the transition from hcp to monoclinic in the solid C70 is sluggish which may cause the broadening in the transition. Our mean-field calculation in this paper, using the Landau free energy functional, indicates that the sluggishness originates from the growing interface due to the elastic strain between the two phases