Intercalation of Acceptors and Donors in Highly Ordered Graphite Fibers
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Mat. Res.
Soc. Symp. Proc. Vol. 20 (1983) @Elsevier Science Publishing Co.,
Inc.
52 dependence is found in both pristine and intercalated BDF (THT = 29000 C). A room temperature conductivity within a factor of 4 of that of copper is found in certain air-stable intercalated fibers. Furthermore, the lattice fringe imaging technique provides direct evidence for large regions (up to 50 A x 400 A) of defect-free single-stage regions, consistent with the high conductivity and metallic temperature dependence found in these intercalated fibers. It is also of interest to note that in the BDF host, it is possible to prepare stage 1 GIC with the intercalants COC1 2 , NiCl 2 which have not been previously prepared with highly oriented pyrolytic graphite (HOPG) or single crystal graphite hosts. EXPERIMENTAL The pristine graphite fibers used in this study were benzene-derived fibers 0 0 [1,2] heat treated at temperatures of 2900 C and 3500 C. For heat treatment to 29000C, the original carbon fibers were placed for 30 minutes in a carbon tube
resistance furnace with a high purity argon atmosphere. For heat treatment between 2900 0 C and 3500 0 C, the fibers were placed in an induction furnace with fine grained graphite serving as susceptor and sample holder [5]. The intercalation of various acceptors FeCl 3 , CoCl 2 and NiCl 2 into BDF with heat-treatment temperature (THT) of 2900*C and the donor KHg into BDF with THT - 3500*C was performed using the two-zone growth method previously developed for the intercalation of acceptors and donors into various graphite hosts [8-10]. The reaction ampoule was left in the two-zone furnace long enough to obtain well staged samples. In fact, samples grown in the furnace for less than a week usually showed unintercalated regions [based on the presence of the (002) x-ray diffraction line of graphite]; it is especially necessary for intercalation of the donor KHg into BDF to keep the growth temperature stable for more than a two-week period. Of particular interest is the successful synthesis of stage 1 GIC in BDF hosts (THT - 29000 C) with the acceptors FeCl 3 , CoC1 2 and NiCI 2 ; in the case of CoC1 2 and NiCI 2 , this appears to be the first successful synthesis of a stage 1 compound. In this synthesis, the method of Stumpp was used [101. After removal from the furnace, the intercalated fiber samples were carefully transferred under a controlled argon atmosphere within a glove box into different sample holders for designated experiments.
For the Debye-Scherrer
x-ray measurements of the c-axis repeat distance Ic, bundles of fibers were encapsulated in a 0.5 mm pyrex tubing and Cu Ka or Cr Ka radiation was employed. For Raman scattering measurements, samples were encapsulated in a rectangular thin wall pyrex tubing; the output signal at the photomultiplier tube was collected using a photon counter and the data were recorded by a multichannel analyzer. The lattice images were obtained using a JOEL 200CX electron microscope with high resolution pole pieces (C. = 2.6 mm) and a LaB 6 filament.
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