The theory of the thermal expansion of diamond

Summary

A modification of the Grüneisen formula for the force between the atoms, suggested by the Morse function, has been used to evaluate the Grüneisen constants of the eight vibration frequencies of diamond given by the Raman dynamics of crystal lattices. It has been assumed that the force constantK _α of the angular distortion does not change, with the change of the crystal volume. The thermal expansion of diamond is then calculated and shown to be in good agreement with the measurements at low temperatures, quoted by Grüneisen and with the experimental data at high temperatures, of Dr. R. S. Krishnan. Nayar’s spectroscopic observations on the change of the Raman line of diamond with temperature have been quantitatively explained. The heat of vaporisation of diamond has been computed and shown to be in reasonable agreement with the value estimated from other considerations.