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Research And Development On Advanced Graphite Materials. Volume XX - The Electric And Magnetic Properties Of Pyrolytic Graphite

Report Number: WADD TR 61-72 Volume 20
Author: Wagoner, G.
Author: Eckstein, B. H.
Corporate Author: Research Laboratory of National Carbon Company Division of Union Carbide Corporation
Laboratory: AF Materials Laboratory
Date of Publication: 1963-11
Pages: 28
Contract: AF 33(616)-6915
Project: 7350
Task: 735002
AD Number: AD0426185

This paper concerns the electric and magnetic properties of a series of highly turbostratic pyrolytic graphic deposits. The diamagnetic susceptibility, Hall coefficient, and electron spin resonance g value are observed to have much larger magnitudes than corresponding measurements made on single crystals of graphite. The results are interpreted as being due to the turbostratic character of the deposit which brings about a decreased interaction between the randomly rotated graphitic planes. The overlap of the electron and hole bands is thereby reduced and as a first approximation one can interpret the results using the simple two dimensional model of Wallace. McClure's diamagnetism formula, which is based on the Wallace model, yields a maximum trace value of -39 emu/g. The largest observed value is -33.5 emu/g, a diamagnetism almost 50 per cent greater than the normal single crystal value of -22.8 emu/g.

To obtain from theory the large variation of g shift and diamagnetism as a function of formation temperature, it is necessary that acceptors be present whose concentration decreases as the temperature of formation increases. Similar acceptors have been postulated by others to explain the properties of high temperature carbons.

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