Stochastic model of stage transformation in graphite intercalation compounds

A stochastic model is presented for stage transformation in graphite intercalation compounds. By introducing three types of intercalation processes into the domain model of Daumas and Hérold, we derive a nonlinear Langevin equation which describes the stochastic motion of intercalant islands. Results of simulation of the Langevin equation show that the stage transformation proceeds via initial nucleation of new stage regions followed by their growth. When the chemical potential of intercalants in the final state, f, is taken in a certain range in the phase diagram, the time evolution of the structure factor demonstrates the coexistence and no significant broadening of peaks corresponding to the initial and final stage structures, in good agreement with experimental results. For other values of f, the system transforms to the final stable stage via an intermediate disordered state or stays in a mixed state of stable stage and metastable stage. The appearance of metastable fractional stage units in the final state of the transformation is discussed.