Using ab initio calculations, the stability issues of a series of Heusler alloys Ni2Mn1+xSb1-x (x=0, 0.25, 0.5, 0.75, 1) with staggered and layer-by-layer ordering of Mn atoms are investigated. It is shown that compositions with an excess of Mn are stable with respect to decomposition into constituent elements and unstable with respect to decomposition into a two-phase system consisting of a ferromagnetic cubic L21-phase Ni2MnSb and an antiferromagnetic tetragonal L10-phase NiMn. Thus, all nonstoichiometric compositions in the austenite and martensitic phases, taking into account different magnetic and atomic ordering, tend to segregate. Stability of alloys is possible only in stoichiometric compositions (x=0 and 1). Keywords: Heusler alloys, ab initio calculations, segregation, phase stability.
Using ab initio calculations, the stability issues of a series of Heusler alloys Ni2Mn1+xSb1-x (x=0, 0.25, 0.5, 0.75, 1) with staggered and layer-by-layer ordering of Mn atoms are investigated. It is shown that compositions with an excess of Mn are stable with respect to decomposition into constituent elements and unstable with respect to decomposition into a two-phase system consisting of a ferromagnetic cubic L21-phase Ni2MnSb and an antiferromagnetic tetragonal L10-phase NiMn. Thus, all nonstoichiometric compositions in the austenite and martensitic phases, taking into account different magnetic and atomic ordering, tend to segregate. Stability of alloys is possible only in stoichiometric compositions (x=0 and 1). Keywords: Heusler alloys, ab initio calculations, segregation, phase stability.
Using ab initio calculations, the phase stability of modulated and tetragonal martensitic structures in Ni43.75Co6.25Mn43.75(In, Sn)6.25 Heusler alloys with different magnetic order is investigated. The stability against the segregation is considered by a method for generating all possible decay reactions assuming the calculated ground state energies of each composition. It is shown that the highest probable stability under equilibrium conditions is demonstrated by alloys with tetragonal martensitic structure in accordance with reactions: Ni35Co5Mn35In5 → 25Mn + 35Ni + 5Mn2InCo and Ni35Co5Mn35Sn5 → 5CoSn + 35Mn + 35Ni.