The binary Ni-Bi alloys as well as multicomponent materials comprising systems like Ni-Bi-Sn, Ni-Bi-Sb etc. are recently considered as prospective for design of lead-free solders. For that reason various authors focused their attention to the Ni-Bi system thermodynamics. The studies identified five phases in the above system. Two of them (i.e., (Ni) and liquid), were treated as disordered substitutional solutions. The phase NiBi 3 is stoichiometric and a standard two-sublattice model was repeatedly applied to describe its Gibbs free energy, while for the nonstoichiometric NiBi phase, a three-sublattice model was retained. The pure bismuth phase ((Bi)) is stoichiometric as well. The results are discussed and compared to literature thermochemical and topological data. In liquid state, strong repulsions between nickel and bismuth atoms are anticipated in the nickel rich-side, but no data about a liquid phase miscibility gap is available yet. Therefore, the stability of the liquid phase has to be reassured, in spite of positive deviations from ideal behaviour.

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