PHASE SELECTION AND TRANSFORMATION KINETICS IN KC60

Phase selection in the 205-500 K range and the kinetics of phase trans formations are studied by differential scanning calorimetry in KC60. T he long-time phase selection is compatible with the Gibbs free energie s determined previously. The Avrami exponent (n=1.9+/-0.1) found for p olymerization is consistent with two-dimensional polymorphic growth at a fixed number of sites. In the 320-380 K temperature range, polymeri zation is coupled with phase separation of a volume fraction (0 to sim ilar to 40%) increasing with temperature. Between similar to 380 and 4 40 K, the phase separation takes place by diffusion-controlled three-d imensional growth accompanied with heterogeneous nucleation approachin g site saturation.