Mössbauer analysis of the acceptor site for the donated electrons in FeCl3-intercalated graphite compounds

Abstract

Recently it has been shown that electrons donated by the graphite host to the FeCl3 intercalate freeze onto selected Fe3+ ions to change them into Fe2+ ions at low temperatures. We find that this process occurs continuously beginning at approximately 100 K. Two possible explanations of the data are presented. We examine the possibility that the number of donated electrons which are associated with selected iron sites is temperature dependent, and that a free-bound transition occurs as the temperature is lowered. We also discuss an alternative explanation first suggested by Hohlwein et al. in terms of a temperature-dependent hopping rate for the electrons which becomes slow compared with the nuclear Larmor frequency at low temperatures. Although our fits to the experimental spectra appear to favor the first explanation, we find that the second one cannot be ruled out on the basis of Mössbauer spectroscopy alone. Finally, we also discuss the sample dependence of the number of Fe2+ sites observed at low temperatures. Our findings support the suggestion of Wertheim et al. that chlorine atoms surrounding iron vacancies when present in sufficient numbers in the intercalate may act as the primary acceptor site for the electrons donated by the graphite to the intercalate. © 1983 The American Physical Society.