Specific Heat of Various Graphites between 0.4 and 2.0°K

Abstract

Below 1.2°K, the specific heat of natural Madagascar graphite is: $C=13.8\mathrm{}T+27.7\mathrm{}{T}^3$ μJ/mole deg. The coefficient of the linear term agrees well with theoretical calculations of the electronic specific heat of a pure single crystal of graphite. The $T^3$ term yields a Debye parameter, ${\Theta }_0$, of 413°K. For pile graphite, lamp-black, and pyrographite it is found that the specific heat is directly dependent on the degree of stacking faults. This is in agreement with the theory which proposes that stacking faults will decrease the value of $c_{44}$, the elastic constant of shear between neighboring layers, which leads to additional modes at low temperatures and thus adds to the specific heat.