Evidence of Single-Crystal Characteristics in Highly Annealed Pyrolytic Graphite

Abstract

It is demonstrated that massive specimens of pyrolytic graphite heat-treated at 3600\ifmmode^\circ\else\textdegree\fi{}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\ifmmode\times\else\texttimes\fi{}${10}^{4}$ ${\mathrm{cm}}^{2}$/v-sec at 300\ifmmode^\circ\else\textdegree\fi{}K; up to 8\ifmmode\times\else\texttimes\fi{}${10}^{5}$ ${\mathrm{cm}}^{2}$/v-sec at 4.2\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K, but departs at lower temperatures. Plausible interpretations of this discrepancy and of the "knee" in the resistivity curve are briefly discussed.