Electrical Conductivities of Natural Graphite Crystals

Electrical Conductivities of Natural Graphite Crystals by William Primak, L. H. Fuchs.

The principal electrical conductivities (${\ensuremath{\sigma}}_{a}$ in the basal plane and ${\ensuremath{\sigma}}_{c}$ perpendicular to plane) of graphite crystals isolated from several North American marbles were studied. By means measurements potential distributions on surfaces carrying electric current, it was conclusively shown that $\frac{{\ensuremath{\sigma}}_{a}}{{\ensuremath{\sigma}}_{c}}$ for these is about hundred at room temperature. direct measurement ${\ensuremath{\sigma}}_{a}$ found be (2.6\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{4}$ (ohm ${\mathrm{c}\mathrm{m})}^{\ensuremath{-}1}$ vary 150 230 (\ifmmode\pm\else\textpm\fi{}20 percent) Below temperature two increased slowly liquid nitrogen temperatures, then followed a ${T}^{\ensuremath{-}1}$ law 15\ifmmode^\circ\else\textdegree\fi{}K, again region 15\ifmmode^\circ\else\textdegree\fi{}K 4.2\ifmmode^\circ\else\textdegree\fi{}K. Two other which measured low temperatures did not behave alike. For both, decreased as lowered, reached minimum above started increasing, one showing behavior, increasing more slowly. rate increase declined markedly

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