Low-Temperature Specific Heat and Density of States of Boronated Graphite

The increase in the low-temperature specific heat upon boronation of natural Madagascar flake graphite has been measured. For the pure material below 1.2°K, $C=13.8T+27.7\mathrm{}{T}^3$ μJ/mole deg; for the same graphite boronated to 0.23 at.%, $C=34.5T+29.3\mathrm{}{T}^3$ μJ/mole deg. The change in electronic density of states at the Fermi surface is found to agree well with theoretical expectation. These results allow one to predict the Fermi-level shifts that would be necessary to account for the increased linear specific heat of disordered graphites. However, the Fermi-level shifts so predicted would require much larger changes in other electronic properties than are actually observed. Thus, the excess specific heats cannot be explained as being due to Fermi-level shifts.