Evidence of Single-Crystal Characteristics in Highly Annealed Pyrolytic Graphite

It is demonstrated that massive specimens of pyrolytic graphite heat-treated at 3600°C may exhibit electrical characteristics comparable to those of the best single crystals presently available. Low-field magnetoresistance data taken perpendicularly to the $c$ direction of these specimens yield average carrier mobilities (1.3×${10}^4$ ${\mathrm{cm}}^2$/v-sec at 300°K; up to 8×${10}^5$ ${\mathrm{cm}}^2$/v-sec at 4.2°K) in substantial agreement with Soule's and McClure's results for the layer planes of highly purified natural graphite. In conjunction with temperature dependence studies of the zero-field resistivity, it is found that the carrier density reproduces the theoretically predicted behavior down to 77°K, but departs at lower temperatures. Plausible interpretations of this discrepancy and of the "knee" in the resistivity curve are briefly discussed.