X-ray intensity calculation in alkali-metal graphite intercalation compounds: Discommensuration-domain model

X-ray intensity calculations of the high-stage (≥2) alkali-metal graphite intercalation compounds are presented on the basis of the discommensuration-domain model in which the basic alkali structure is a registered (√7 × √7 )R${19.11}^{°}$ lattice with large hexagonal domains and regular phase slips. The observed x-ray diffraction patterns exhibit pronounced features: (1) an unusual intensity variation around the graphite (100) peak and (2) a universal curve relating rotation angle to the wave vector of the fundamental mass-density wave in the alkali-metal layer. Through model calculations, these features are found to give direct evidence for the discommensuration-domain model.