Sluggishness in the phase transformation in solid C70

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 similar to 1.63) solid C-70 transforms to a monoclinic structure, in a single step. The transition is broadened over a temperature interval of about 100 K, for a cooling rate similar to 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 C-70 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. (C) 2000 Elsevier Science Ltd. All rights reserved.