Experimental Chemistry and Structural Stability of AlNb₃ Enabled by Antisite Defects Formation.

First-principles evolutionary algorithms are employed to shed light on the phase stability of Al⁻Nb intermetallics. While the tetragonal Al₃Nb and AlNb₂ structures are correctly identified as stable, the experimentally reported Laves phase of AlNb₃ yields soft phonon modes implying its dynamical instability at 0 K. The soft phonon modes do not disappear even upon elevating the temperature in the simulation up to 1500 K. X-Ray diffraction patterns recorded for our powder-metallurgically produced arc cathodes, however, clearly show that the AlNb₃ phase exists. We propose that AlNb₃ is dynamically stabilised by ordered antisite defects at the Al sublattice, leading also to a shift of the Nb content from 75 to ∼81 at.%. Unlike the defect-free AlNb₃, the antisite-stabilised variant hence falls into the compositional range consistent with our CALPHAD-based phase diagram as well as with the previous reports.