Specific Heat of Diamond at Low Temperatures

Specific heat data on diamond at temperatures between 20° and 300°K are reported. Comparisons of the data have been made with the predictions of the Debye theory. The deviation of the specific heat from the value given by the three-dimensional continuum theory in the low temperature region can be qualitatively described in terms of a superposition of a simple Einstein frequency. It has been found that variations that occur in expressing reduced characteristic temperatures as a function of reduced temperatures for diamond are qualitatively similar to those of the face-centered cubic metals Al, Cu, and Ag. The values of entropy, enthalpy, and free energy have been determined and tabulated at integral values of temperature from 25° to 300°K. The entropy of diamond at 298.16°K is 0.568±0.005 cal/g-atom/deg.