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S. Yu. ZAGINAICHENKO, Z. A. MATYSINA, and D. V. SHCHUR
«Phase Transformations and Heat Capacity in Fluorofullerene Crystals»
PACS numbers: 61.46.Hk, 61.48.De, 61.72.Bb, 64.60.Cn, 64.75.Gh, 65.40.Ba, 81.05.ub
On the basis of molecular-kinetic conceptions, the theory of order–disorder phase transition is developed for the mixture of fluorofullerenes: transition from the ordered b.c.t. structure to the disordered f.c.c. structure. The free energies of these phases are defined, their dependences on temperature, composition of material, the degree of order and energy constants are determined. The temperatures of phase transitions are calculated. The constitution diagram is plotted. This diagram determines the temperature and concentration areas of b.c.t. and f.c.c. phases formation as well as the region of concurrent realization of both b.c.t. and f.c.c. phases. The configuration heat capacity of b.c.t. phase and its temperature dependence are determined. The peak-shaped increase of heat capacity in the vicinity of the temperature of phase transition is shown, and this fact is consistent with experiment.