Island Growth and Orientational Locking of Potassium Intercalated in Graphite

Island growth and orientational locking in stage-2 potassium-intercalated graphite is observed by real-space imaging and electron diffraction on single crystallites. A mechanism is presented, relating these two phenomena. For $86\lesssim T\lesssim 130$ K, intercalate islands of incommensurate ordering are orientationally unlocked from the graphite lattice, as indicated by ring diffraction patterns. With increasing temperature, gradual island growth is by accretion. A threshold size (∼50 Å reached at 130 K) triggers precipitous island growth by coalescence and orientational locking.