Electronic structure and magnetic properties of Fe₃C with 2p and 3p impurities

Abstract

Ab initio calculations were performed to determine the effect of 2p and 3p impurities on the structural, electronic, and magnetic properties of cementite. We predict that phosphorus, sulfur, and all 2p impurities replace carbon, while aluminum and silicon substitute for iron. The magnetization and magnetic moments on iron atoms in the special and general positions only slightly change for impurities in the carbon sites, but they essentially decrease for impurities that substitute for iron (Al, Si). We find that boron and nitrogen (to a lesser degree) promote the stabilization of cementite and may be dissolved with the formation of ternary Fe3(C, B) and Fe3(C, N) cementites. Aluminum and especially silicon sharply suppress the formation of cementite.

Nitrogen controlled iron catalyst phase during carbon nanotube growth

“…5 Equally, during exposure to the hydrocarbon source in the growth stage (orange trajectory (III) in Figure 3(c)), we observed phase-pure Fe 3 C catalyst particles when using NH 3 (in contrast to the c-Fe/a-Fe/Fe 3 C mixtures when using H 2 5 ). Thus, co-feeding of nitrogen also drastically changed the phase evolution of the catalyst during the growth stage, indicating that nitrogen addition stabilizes Fe 3 C. This observation is in good agreement with previously published phase stabilities in the ternary Fe-C-N system as a function of nitrogen and carbon activities ("Lehrer diagrams") 52,53 and also with recent first principle calculations on the stabilizing effect of N addition on Fe 3 C. 54 Our own thermodynamic calculations in Figure 3(c) also show that the phase fraction of Fe 3 C is incrementally increasing by N addition for a range of C contents. We note however that while the Fe 3 C fraction in the c-Fe/Fe 3 C two phase field incrementally increases with N content, we do not calculate a phase-pure Fe 3 C region in the considered (C,N) compositional range (unlike for c-Fe).…”

First-Principles Calculations on Stabilization of Iron Carbides (Fe3C, Fe5C2, and η-Fe2C) in Steels by Common Alloying Elements

“…Al is most stable on the Fe2(8d) site. The preference of Al, Si for the Fe site and P, S for the C site from our 2 9 2 9 2 supercell calculations agree well with previous results, [22] which were carried out at a lower kinetic energy cutoff (350 eV).…”

“…[12] The energetics and electronic structure of impurity substituted cementite have also been the focus of a considerable number of previous studies. [11,[18][19][20][21][22][23][24][25][26][27][28][29][30] The partitioning behavior of alloying elements between cementite and ferrite has been described, [31] and the stabilization of cementite by various alloying elements has been studied. [20][21][22][23][24][25][26][27][28][29][30] In most previous computational work on the stabilization of carbide phases by alloying elements, conclusions were based on enthalpies of formation with respect to the pure carbide phase.…”