Lattice Constants of Graphite at Low Temperatures

The lattice constants of a graphite single crystal, natural graphite powder, and artificial graphite powder have been measured at 297^∘{}K, 78^∘{}K, and 4.2^∘{}K. The a-spacing does not change in this temperature range within the error of ±{}0.0005 A. The material with the greatest c-spacing showed between 297^∘{} and 78^∘{} the greatest change of c-spacing and the smallest change below 78^∘{}. The c-spacing of the artificial powder did not return to its original value at 297^∘{} after a thermal cycle, demonstrating irreversible deformation.