It was recalled that the formation and migration energies of defects were studied routinely using first-principles calculations. However, they were usually studied using static zero-temperature calculations, and the entropic contributions to the free energies were completely neglected. Here, first-principles calculations were made of the vibrational part of the free energies of formation and migration of silicon and carbon interstitials in silicon carbide. It was found that formation free enthalpies could vary by up to 1eV, in the range from 0 to 2000K, while migration free energies varied by only a few tenth of an electron volt. The results furnished not only the activation energies for diffusion but also the diffusion pre-factors. The comparison with experimental results showed good agreement for carbon self-diffusion while for silicon self-diffusion the results underestimated by three orders of magnitude the experimental values, suggesting that defects other than the interstitials were the dominant diffusing species.

Activation Entropies for Diffusion in Cubic Silicon Carbide from First Principles. O.N.Bedoya-Martínez, G.Roma: Physical Review B, 2010, 82[13], 134115