F. Lincoln Vogel

The electrical conductivity of graphite intercalated with superacid fluorides: experiments with antimony pentafluoride

The electrical conductivity in graphite measured normal to the crystallographic c-axis is observed to increase after intercalation with acid molecules which act as acceptors. This behaviour is regarded as the result of ionization of the acid molecule which, in turn, increases the positive current carriers in the host graphite. Since the carrier density depends on the degree of ionization of the acid, it follows that the stronger the acid the greater the increase in carrier concentration, and assuming no adverse mobility effects, the greater the electrical conductivity. The hydrogen fluoride-antimony pentafluoride system produces some of the strongest acid substances known. The experiments described here represent the initial examination of the electrical conductivity resulting from intercalation of this material into graphite. The experiments consisted of intercalating graphite powder with antimony pentafluoride in a copper tube and swaging the sheathed compound into wire. The measured conductivity of the graphite intercalation compound, when the copper conductivity is subtracted out and allowance is made for departure from ideal density, is about 1×106 Ω−1 cm−1. This is approximately 40 times the conductivity of pristine graphite and more than one and a half times the conductivity of pure copper.The electrical conductivity in graphite measured normal to the crystallographic c-axis is observed to increase after intercalation with acid molecules which act as acceptors. This behaviour is regarded as the result of ionization of the acid molecule which, in turn, increases the positive current carriers in the host graphite. Since the carrier density depends on the degree of ionization of the acid, it follows that the stronger the acid the greater the increase in carrier concentration, and assuming no adverse mobility effects, the greater the electrical conductivity. The hydrogen fluoride-antimony pentafluoride system produces some of the strongest acid substances known. The experiments described here represent the initial examination of the electrical conductivity resulting from intercalation of this material into graphite. The experiments consisted of intercalating graphite powder with antimony pentafluoride in a copper tube and swaging the sheathed compound into wire. The measured conductivity of the graphite intercalation compound, when the copper conductivity is subtracted out and allowance is made for departure from ideal density, is about 1×106 Ω−1 cm−1. This is approximately 40 times the conductivity of pristine graphite and more than one and a half times the conductivity of pure copper.

Electrical resistivity and X-ray spacings of graphite tetrafluoroborate, hexafluorophosphate and hexafluoroantimonate compounds synthesized from nitronium salts

Abstract The action on graphite of the nitronium salts NO2BF4, NO2PF6, and NO2SbF6 dissolved in dry nitromethane has led to the formation of novel intercalation compounds. These compounds have been synthesized in a wide variety of states and characterized with respect to X-ray identity period along the c - axis , electrical resistivity normal to the c - axis , and thickness and weight change.

Intercalation of pyrographite by NO2+ and NO+ salts

Abstract BF 4 − , PF 6 − and SbF 6 − ions have been intercalated into pyrographite HOPG by chemical oxidation. The graphite is oxidized by NO 2 + (or NO + in certain experiments) coming from NO 2 BF 4 , NO 2 PF 6 and NO 2 SbF 6 (or NOSbF 6 ) salts dissolved in dry nitromethane. X-ray diffraction allows us to determine the identity period along the c axis leading to the stage n and the interpianar distance d I . Relative weight change leads us to believe that the MF x − anions are solvated by the solvent. Chemical analyses confirm this hypothesis allowing us to give to these compounds the ideal formula C + 23n MF − x (CH 3 NO 2 ) y .

Very high electrical conductivity in AsF5–graphite intercalation compounds

Arsenic pentafluoride–graphite intercalation compounds of uniform stages 1–3 have been prepared by direct synthesis; very high a-axis electrical conductivities, similar to that of copper, were determined by r.f. (100 kHz) and d.c. techniques.

The synthesis and resistivity of the ternary graphiteKNa compounds

Abstract The ternary compounds K x Na 1− x C y where x is between 0.45 and 1 were synthesized by the contact of graphite crystals and NaK alloys. These compounds were then characterized by 00 l X-ray diffraction spacings, chemical analysis of the ratio of sodium to potassium and the electrical resistivity. Large positive deviations from Vegards law behavior were observed for the potassium-rich compositions. At higher stages, higher concentrations of sodium can be intercalated into the layer with a concomitant reduction in d i . The in-plane electrical resistivities of the graphiteKNa ternary compounds are lower than those of the KNa binary compounds at corresponding stages.

Some potential applications for intercalation compounds of graphite with high electrical conductivity

Abstract Intercalation compounds of graphite of the acceptor type have potential engineering applications because of their attractive electrical conductivity properties. Two kinds of applications are considered in this paper. The first concerns a composite, formed by enclosing an intercalation compound synthesized from high quality crystalline graphite in a matrix of copper. With this form of composite it is found that there are both intrinsic and extrinsic advantages pertaining to the use of a material that has a conductivity higher than and a density lower than that of copper. The second form is a composite compound of intercalated graphite fibers contained in a matrix of epoxy. Extraordinary advantages in this case result from the fact that while intercalation of the fibers produces an order of magnitude increase in their electrical conductivity, when these fibers are incorporated into an epoxy matrix, the composite conductivity is increased by two orders of magnitude over its pristine fiber counterpart. It is projected that these desirable electrical conductivity characteristics portend large scale uses for the acceptor compounds of graphite as substitutes for the present standard conductors, and as a way of upgrading the performance of carbon/graphite materials.

Synthesis and resistivity as a function of composition and stage for some ternary intercalation compounds

Abstract The reaction of metallic A a B b alloys with graphite, by direct contact or by vapour phase, usually leads to the formation of ternary intercalation compounds when both A and B are able to intercalate into graphite or when A or B is able to intercalate and if bondings exist between A and B. Thus, K a Cs b alloys, where K and Cs easily give well known intercalation compounds, react with graphite to give the K x Cs 1− x C 8 ternaries ( 0 ⪕ × ⪕ 1 ) which are solid solutions of KC 8 and CsC 8 . Study of the 001 X-ray reflections which allows us to determine the interplanar distance, d I , shows that the curve d I vs . × presents large deviations from Vegards law. Resistivity measurements as a function of x show that this parameter is about the same in these ternaries and in the corresponding binaries KC 8 and CsC 8 . The reaction of K a Na b and K a Tl b alloys with graphite also leads to the formation of ternary compounds, even if Na intercalates only with difficulty and if Tl does not intercalate alone. The existence of definite alloys between K and Na or K and Tl indicates the formation of bondings that are partially maintained during the intercalation, allowing Na and Tl to be “drawn” in with K in the sheets of graphite. In particular conditions, ternaries K x Na 1− x C y and K x Tl 1− x C y may be obtained with 0.45 ⪕ × ⪕ 1 and 0.85 ⪕ × ⪕ 1 , respectively. X-ray analyses indicate that both these ternaries are solid solutions and that the interplanar distance d I does not follow Vegards law. The resistivity is lower in these ternaries than in the corresponding binaries.

Intercalation Compounds of Graphite

Intercalation compounds of graphite are of interest, both scienfically and technologically because of unusual properties that derive mainly from high degree of crystal anisotropy. This structure, composed of atoms tightly bonded in loosely stacked planes, produces a two dimensionality that yields a high in-plane strength and elastic modulus, high electrical conductivity, selective catalytic and chemical reactions and other interesting phenomena. Since a wide range of variables can control these effects, the materials scientist is afforded an opportunity for the design of synthetic materials rather than relying upon the limited properties of natural materials. Thus in this conference on molecular metals the exposure of unconventional properties is to be expected. The science of materials that produces this design information lies at the juncture of chemistry and physics, employing the former for the intelligent synthesis of materials and the latter for rationalization of properties. This paper will present intercalation compounds of graphite from the point of view of a quest for a synthetic material of high electrical conductivity.

Electrical resistivity and magnetoresistance of carbon/graphite fibers intercalated with nitric acid and arsenic pentafluoride

A series of high performance, experimental carbon/graphite fibers was intercalated and examined with respect to their metallic conductivity behavior by resistivity and magnetoresistance versus temperature measurements. One fiber was a polyacrylonitrile (PAN)-type precursor and three were pitch base precursors. All four types showed substantially similar behavior in the pristine state with respect to room temperature resistivity and the sign and magnitude of the temperature coefficient of resistivity. After intercalation with either nitric acid or nitric acid followed by AsF5, the PAN-based fibers displayed a resistivity versus temperature behavior qualitatively similar to their pristine counterparts but displaced to lower resistivity. On the other hand, the pitch fibers with the same intercalation treatment exhibited metallic behavior (a positive temperature coefficient of electrical resistivity and a small magnetoresistance). These manifestations of metallic behavior are usually indicative of some three dimensional graphite structure in the carbon fibers.

Electrical Conductivity and Superconductivity in Graphite Intercalation Compounds

This paper will provide a current review of the electrical conductivity of the donor and acceptor intercalation compounds of graphite based on the research of the group at Penn and their collaborators.