First-principles simulation of an ordered sigma phase of the Fe-Cr system in the ferromagnetic state

Abstract

Results of a first-principles simulation of the σ phase of the Fe-Cr system performed using a WIEN2k program code in the generalized-gradient approximation for the exchange-correlation potential are given. The work was aimed at the determination of equilibrium states and energies of formation of the ferromagnetic state of the σ phase of the Fe-Cr system, whose structure (space group no. 136) was examined in the form of ordered configurations A 2 B 4 C 8 D 8 E 8, where A, B, C, D, and E are the crystallographic nonequivalent atomic subgroups, and the subscripts indicate their size (number of atoms). The calculations performed show that two most stable configurations Fe 2Cr4Fe8Fe8Cr8(x Cr = 0.40) and Fe2Fe4Cr8Fe 8Cr8(x Cr = 0.53) in the ferromagnetic state are more stable than in the nonmagnetic state. The influence of ferromagnetism on the value of the energy of formation calculated relative to the pure components in their thermodynamically stable states is especially noticeable in the case of the configuration Fe2Cr4Fe8Fe 8Cr8 (x Fe = 0.60) (approximately 6.36 kJ/mol). In this case, the average atomic magnetic moment was approximately 0.75 μB. The results of the first-principles calculations (at 0 K) of the energies of formation and magnetic moments of the ordered configurations of the σ phase satisfactorily agree with the available experimental data. © 2009 Pleiades Publishing, Ltd.