Kinetics of staging transitions: A neutron diffraction study of pressure-quenched potassium-intercalated graphite

Computer simulations of constant-density staging transitions induced by quenching from high temperature show interesting kinetic effects, but on a very short time scale. We performed analogous pressure quenches from zero to 10--15 kbar at 300 K in an attempt to slow down transient processes and reveal the time dependence. However, we found no time-dependent effects for 2 min <t<5 days. The 300 K P-induced transitions are much faster than the corresponding high-T transitions during intercalation, suggesting that the constant-density process is nucleation controlled rather than diffusion limited. A dilute sample shows the same high-P phases after fast or slow pressurization, while KC₂₄ shows much more disorder when quenched, including some stage-4 cells which do not occur in the ``adiabatic'' case. We suggest that the unique quenching behavior of the stage-2 phase is related to the discommensuration-domain in-plane structure.