Neutron Diffraction Studies of Graphite−Potassium−Methylamine: Staging Transitions and Structure of New Graphite Intercalation Compounds

Abstract

Graphite intercalation compounds (GICs) of the type KCx(CH3NH2)y have been prepared by in situ amination of stage-II C24K and stage-IV C48K, and studied by time-of-flight neutron diffraction. As the vapor pressure of methylamine is increased the compounds pass through a rich sequence of staging transitions, in which the regular repeat of n empty graphite layers is progressively filled by intercalant. In these staging transitions, n always changes by −1. We therefore observe lower stage unaminated compounds as methylamine is introduced into the starting compounds. Isotopic substitution of CD3ND2 for CD3NH2 has enabled us to determine the detailed structure of the fully aminated stage-I and stage-II end compounds, C24K(CH3NH2)3 and C48K(CH3NH2)3. We find that the interlayer structure is based on 3-fold coordinated potassium ions and is relatively insensitive to the stage.