Stability, structure and electronic properties of gamma-Fe23C6 from first principles theory

First-principles' calculations of GGA and GGA - U type have been performed for gamma-Fe23C6, a complex iron carbide with 116 atom in the unit cell GGA results were found to be in better agreement with experimental data than GGA + U results Various occupancies for Wyckoff positions and corresponding magnetic orderings have been explored Our calculations reveal that the crystal structure is composed of a framework of strongly linked Fe atoms, and additional stabilizing Fe and C atoms positioned in cavities The local electronic and magnetic properties vary strongly among the non-equivalent Fe sites in gamma-Fe23C6 The lattice parameters of gamma-Fe23C6 match those of austenite well Surprisingly, pure gamma-Fe23C6 is found to be more stable than commonly occurring theta-Fe3C cementite Moreover, the calculations show low vacancy energy (about 0 37 eV) for Fe at 4a sites in gamma-Fe23C6 Conditions of formation and factors hampering the formation of gamma-Fe23C6 in steel manufacturing processes are discussed