The thermopower of three exfoliated graphites (Grafoil, Foam, and UCAR-$\mathrm{ZYX}$) has been measured in the temperature range 1.7-300 K. Around 30 K a large negative anomaly similar to that of highly oriented pyrolytic graphites is observed. At higher temperatures the thermopower of all exfoliated graphites is, however, more positive. This may be a consequence of a small acceptorlike residuum remaining in the samples after the exfoliation process. Thermopower of $\mathrm{ZYX}$ graphite has been tentatively separated into its diffusion and phonon-drag components.

• Received 23 October 1981

DOI:https://doi.org/10.1103/PhysRevB.25.4167