Energetics, electronic structure, and positron annihilation studies of carbon-vacancy complexes in iron

• Published in: Zeitschrift f r Physik B Condensed Matter 1990-06, Vol.81 (2), p.281-289
• Main Authors: Press, M. R., Khanna, S. N., Jena, P., Puska, M. J.
• Format: Article
• Language: English
• ISSN: 0722-3277; 1434-6036
• DOI: 10.1007/BF01309360

Using the density functional theory and the embedded cluster model the energetics of carbon--vacancy complexes in Fe have been calculated as a function of distance separating the C atom(s) and the vacancy along different crystallographic directions. Carbon is found to prefer off-center sites from the vacancy and maintains a constant distance of approx 3.35 a sub o from the nearest Fe atom(s) independent of its direction from the vacancy center. This distance agrees closely with that in stoichiometric Fe sub 3 C. The results suggest that the equilibrium site of C is one where it is coordinated to three Fe atoms in its nearest neighbor shell. Further decoration of vacancies by more than one C atom has been found to be energetically favourable. The binding of C to Fe atoms is not caused by a charge transfer between the atoms, but rather has a magnetic origin. Positron lifetimes at vacancies and vacancy--carbon complexes have also been calculated for various configurations. The results are in general agreement with experiment. Graphs. 23 ref.--AA