Ab initio calculations of lattice stability of sigma-phase and phase diagram in the Cr–Fe system

Total energy of pure metals in the sigma-phase structure and in the standard element reference (SER) structure were calculated by full-potential linear augmented plane waves method in the general gradient approximation at the equilibrium volume of all phases. Relaxation of lattice parameters of sigma-phase and SER structure were performed. The difference of total energy of sigma-phase and of standard element phase for pure constituents (Δ0Eiσ–SER) was used in a new two-sublattice model of sigma-phase, which was subsequently employed for calculation of phase diagram. y term of Gibbs energy of elements in sigma-phase structure and excess Gibbs energy of mixing of sigma-phase have still to be adjusted to the experimental phase equilibrium data. This procedure was tested on the Fe–Cr system.