Ground-state and thermal properties of substituted iron nitrides

Self-consistent hand-structure calculations were performed for substituted iron nitrides at several lattice parameters using the linear muffin-tin orb ital method (LMTO) in the local spin density approximation. In particular, four compounds were analyzed, namely Fe4N, PdFe3N, MnFe3N and SnFe3N. The c alculations were performed in both ferromagnetic and non-magnetic states an d the present results include total energy, equilibrium lattice parameter, huh; modulus and critical pressure. From the results for the critical press ure we conclude that the above compounds show Invar-like behavior. For smal l total energy separation between ferromagnetic and non-magnetic states at zero temperature. we performed free energy calculations including lattice a nd electronic contributions to study the thermal expansion of the compound employing a simple two level model. (C) 2000 Elsevier Science S.A. All righ ts reserved.