In situobservation of staging in potassium-graphite intercalation compounds

Stage transformations in the potassium-graphite intercalation compound have been studied by in situ x-ray diffraction. A precise phase diagram has been determined for the stages up to 7. The stage dependence of Δμ(n), the stable range of a given stage n in chemical potential, is evaluated from the phase diagram and compared with the theoretical results for the electrostatic model for staging. Time-dependent observation of the stage transformation reveals that only two phases of adjacent stages coexist throughout the process of the stage transformation so that the c-axis disorder is insignificant even in the transition region. The kinetics of the stage transformation is also discussed.