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The lattice constants of a graphite single crystal, natural graphite powder, and artificial graphite powder have been measured at 297^, 78^, and 4. 2^. 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.
Baskin et al. (Sat,) studied this question.