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 FeC13 intercalate freeze onto selected Fe'+ ions to change them into Fe + 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 a/. 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 experirnental spectra appear to favor the first explanation, we find that the second one cannot be ruled out on the basis of Mossbauer spectroscopy alone. Finally, we also discuss the sample dependence of the number of Fe + 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.

Spin-glass phases in stage-2FeCl3graphite intercalation compound

“…16 According to the comment by Millman and Kirczenow, 16 a careful reexamination of the spectra of Ohhashi and Tsujikawa 2 shows that there is a noticeable concentration of Fe 2ϩ present in their sample in spite of their claim. Holwein et al 4 have reported that the percent contribution of Fe 2ϩ is 20% for stage-1 FeCl 3 GIC.…”

“…2,4,[12][13][14][15][16] Millman and Kirczenow 16 have shown that there are three kinds of Fe site in the FeCl 3 intercalate layers of stage-1 and stage-2 FeCl 3 GIC's. Their results for stage-2 FeCl 3 GIC are as follows.…”

“…The magnetic properties of FeCl 3 GIC's have been studied by many researchers for almost three decades. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The pioneering work of the magnetic study on FeCl 3 GIC's was made by Karimov and co-workers. 1 They showed that the magnetic susceptibility of polycrystalline samples has a peak at 3.6 K for stage-1 GIC and at 7 K for stage-2 GIC, which is identified as the onset of antiferromagnetic and ferromagnetic phase transitions, respectively.…”

Magnetic phase diagram and cluster glasslike properties of stage-1 graphite-intercalated FeCl3

“…However, Mössbauer spectroscopy reveals a more complex situation. Three distinct Fe sites (A, B, and C) are found in temperature-dependent Mössbauer measurements [16,17]. The majority component originates from site A and is attributed to Fe 3+ ions [16], the magnetic moments of which lie in the basal plane [16,17].…”

“…Three distinct Fe sites (A, B, and C) are found in temperature-dependent Mössbauer measurements [16,17]. The majority component originates from site A and is attributed to Fe 3+ ions [16], the magnetic moments of which lie in the basal plane [16,17]. This component plays a dominant role in the onset of the low-temperature magnetically ordered state, as only the Fe 3+ ions of site A were found to participate in the magnetic ordering [17].…”