The electronic structure of the ternary donor graphite intercalation compound (DGIC) ${\mathrm{C}}_4$${\mathrm{RbTl}}_{1.5}$ has been studied with various techniques of photoemission. Ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy were used to study the electronic effects of the cointercalation of thallium into the first-stage binary precursor intercalation compound ${\mathrm{C}}_8$Rb. In the ternary DGIC a significant Rb-Tl interaction modifies the charge transfer from the donor alloy to the graphite host. The results indicate a substantial charge transfer from the alkali metal to graphite-derived π states which is reduced upon ternarization. The reactivities of clean surfaces of elemental thallium and of the ternary intercalation compound towards oxidation have been investigated. Different reaction products and pathways of oxidation were found. The experimental data presented suggest that the mechanism of charge transfer is better described in the hybridization model rather than in the approximation of complete ionicity.

• Received 25 July 1986

DOI:https://doi.org/10.1103/PhysRevB.35.6414