A new thermodynamically stable Nb₂Ni intermetallic compound phase revealed by peritectoid transition within binary Nb-Ni alloy system

A new intermetallic compound of thermodynamically stable Nb₂Ni phase is discovered within Nb-Ni binary system, refreshing the current situation that there are only three stable intermediate phases of Nb₇Ni₆, NbNi₃ and NbNi₈. The new stable phase is generated from the peritectoid transition: (Nb) + Nb₇Ni₆ → Nb₂Ni, and the transformation temperature is 1533 K. This refreshes the current equilibrium Nb-Ni binary phase diagram. It is confirmed by transmission electron microscopy and the annealing experiments, which is determined to be the FCC structure (Pearson: cF96, space grope: Fd-3m O2, a = 11.888 Å). Furthermore, the equilibrium properties of Nb₂Ni phase are produced by density functional theory, including the formation energy, cohesive energy, bulk modulus and lattice constant.