FORMATION ENTROPY AND THE DIFFUSION CONSTANT FOR VACANCIES IN CU AND ALPHA-FE

The formation entropy of single vacancies and divacancies and the frequency factors entering in the diffusion constants are calculated for Cu and Fe based on a pair-potential approach. For Cu a Morse and a Born-Mayer potential have been employed, for Fe the potential of Chang and Graham. The calculations have been performed by a determinant method and partly also by the Green's-function method. The effects of the long-range displacements have been carefully estimated and are very important. For the Morse potential the formation entropy is 2.3k for a single and 4.0k for the divacancy in Cu, whereas the temperature-independent part of the diffusion constant is 0.12 and 3.7 cm2/sec, respectively. For Fe, the Chang-Graham potential leads to a formation entropy of 2.1k and to a diffusion constant of 0.16 cm2/sec for single vacancies. © 1979 The American Physical Society.