X-ray determination of the modulation potential in a stage-2 potassium-graphite intercalation compound

By use of both synchrotron and conventional x-ray sources, the HK.L Bragg peaks have been measured at room temperature on a single crystal of graphite, intercalated with potassium to stage 2. For these reflections there is a contribution of the two-dimensional alkali metal liquid due to the modulation induced by the host graphite lattice. Using the theory of Reiter and Moss, we have extracted the modulation potential by fitting the integrated intensities for the H-K=3m reflections and the intensity profiles along L for those reflections where H-K=3m±1. The potential is similar to that derived for Rb in graphite but with enhanced local minima at the carbon atoms. The stacking faults in this crystal are found to occur at random.