Theoretical study of the C-C interaction in the (001) bcc Fe which contain a vacancy

S. SIMONETTI, G. BRIZUELA, E. PRONSATO, A. JUAN

Pardubice Rep. Checa

Congreso; 7th Internacional Congress of the Solid state Shemistry; 2006

Sociedad Europea de Quimica

Interaction of metals with reactive gases during heat treatment often causes an undesired adsorption of impurity atoms. In the opposite hand, the annealing of pure metals and alloys in gas mixtures like CH4-H2 can be useful technique for doping. Several compounds can be formed in metal-gas system by different mechanisms. Compounds can grow on the metal surface or precipitate in the bulk or in the defects of the material and produce embrittlement of polycrystalline materials. Even traces of gases or carbon can be very detrimental for these metals. The C-Fe interaction in the (001) bcc Fe wich contain a vacancy was analyzed using a semi-empirical theoretical method. A cluster model containing 125 atoms was used to simulate the local environment of the Fe vacancy. Carbon atoms were positioned in their local energy minima configurations. The most stable positions for the C atoms in the (001) bcc Fe were found at about 1.2 Å from the vacancy center and near to the first nearest-neighbor octahedral sites. The vacancy and the impurities were almost aligned in the same direction. Changes in the electronic structure of Fe atoms near a vacancy were analyzed for the systems with one and two C atoms. Fe atoms surrounding the vacancy weaken their bond when C is present. This bond weakening is a consequence of the C-Fe bonds' formation. The Fe-C interactions occur mainly via Fe 4s orbitals with a lesser participation of Fe 4p and Fe 3d orbitals. There is an electron transfer to the C atoms from their Fe nearest neighbors. The C-C interaction was also analyzed. For the C-C equilibrium distance of 2.42 Å, there is no possible bonding between the C atoms in the (001) bcc iron. The Fe-C interactions are stronger than any possible C-C interaction