Effect of the carbon isotope composition on the properties of diamond

Abstract

Parameters of the interatomic interaction potential for 12C and 13C carbon isotopes in the crystal lattice of diamond have been determined. Based on these data, the isotope dependence of the properties of diamond such as the Debye temperature, molar heat capacity, thermal expansion coefficient, vacancy formation energy, self-diffusion activation energy, surface energy, and longitudinal sound velocity is described. This approach is used for estimating a change in the bulk compression modulus of lithium crystals upon the passage from 7Li to 6Li. As the temperature increases, the isotope dependence of the heat capacity at constant volume vanishes; at a certain temperature, the isotope dependence of the thermal expansion coefficient changes from growth to decay. The expected isotope dependence of the parameters of phase transitions is predicted. It is shown that carbon condensates formed upon deposition from the gas phase must be enriched with the heavy isotope.