X-ray Study of Intercalate Order-Disorder Transition inC24K

Below $T_c=122.9\mathrm{}$ °K, ${\mathrm{C}}_{24}$K shows a transition from the intralayer disordered state to an ordered state. For $T>\mathrm{}{T}_c$, present diffuse scattering data from the potassium intercalate in graphite indicate a two-dimensional (2-D) character of the short-range order. As this 2-D scattering increases with decreasing temperature, $\mathrm{hk}0\mathrm{}$ superlattice reflections appear at $T_c$ which have a true 3-D character that results from essentially simultaneous intralayer and interlayer ordering. This long-range order vanishes as ${|T-T_c|}^{\beta }$ with $\beta =0.180\mathrm{}\pm 0.01$.