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H. SFIHI, L. FACCHINI, J. BOUAT, D. BONNIN, A.P. LEGRAND Laboratoire de Physique Quantique, ERA N0676 E.S.P.C.I., 10, rue Vauquelin 75231 Paris Cedex 05 FRANCE G. FURDIN, D. BILLAUD Laboratoire de Chimle du Solide Miniral, Service de Chimie Minerale Appliquee du Professeur HNrold, LA N'158, C.O. 140, 54037 Nancy Cedex FRANCE

ABSTRACT 19

F nuclear magnetic resonance and As X-ray absorption results on AsF 5 -graphite intercalation compounds are discussed in terms of species of the commonly used oxidation reaction of the graphitic planes. Three fluorine populations and two oxidation states of the arsenic are clearly present, but they cannot be easily related to the oxidation reaction of the graphite planes.

INTRODUCTION The understanding of the transport properties of graphite intercalation compounds (GIC) is generally related to the knowledge of the chemical state of the intercalated atoms or molecules. This is particularly true for arsenic and antimony fluoride compounds, for which different chemical species may be present in the intercalated layer. Several papers in this symposium give evidence for this phenomenon. We present new results of nuclear magnetic resonance (NMR) and X-ray absorption edge on AsF 5 -GIC. They respectively give information about the fluorine and arsenic populations. They will be discussed and compared to those generally obtained on pentafluoride compounds. The acceptor electrical properties of AsF 5 are usually explained by an oxidation reaction of the graphitic planes: C

+ 3 AsF 5 '_C++ + 2 AsF6 + AsF n 5 n6 3~

1

A similar phenomenon is supposed to occur with SbF 5 . The amount of the different chemical species AsF 5 , AsF and AsF 3 characterizes the charge transfer. Unfortunately, no experiment has given clear evidence for the simultaneous presence of these three species. In first stage samples, previous studies by X-ray absorption edge [1], which are bulk measurements, and XPS [21, which are surface measurements, have shown the existence of one or two valence states of As possibly related to these species, but not necessarily three. In antimony pentafluoride compounds, infrared spectroscopy [3], XPS [3,4] and Sb MH5ssbauer [5,6,71 studies often lead to analogous problems. On the other hand, 19F NMR has shown an evolution with temperature of two fluorine populations with different mobilities in arsenic and antimony pentafluoride GIC [8,9,10]. NMR RESULTS The new results reported here were obtained by a pulsed NMR technique, carried out at 60 and 84 MHz on HOPG first, second and third stage samples intercalated with AsF 5 . The typical Fourier transform obtained from 7, t,

Mat.

Res.

Soc. Symp.

Proc. Vol.

20 (1983) C)Elsevier Science Publishing Co.,

Inc.

7T/2

384 free induction decay sequences is shown on Fig. 1 for a first stage sample. The samples can be rotated in the magnetic field; the figure shows the sequences when the magnetic field is perpendicular to the c-axis. The existence of three lines with different chemical shifts is evident, owing to their different rates of