Although little is known about the influence of phonons on the point defect properties of ordered compounds, experimental measurements (positron annihilation) have pointed out the occurrence of unexpectedly strong effects, especially in iron aluminides. As a complementary approach, the present study, devoted to an atomic-scale simulation study of Al-rich Ni-Al intermetallic phases by means of embedded-atom potentials, aims at providing further insight into the role of this factor, presumably non negligible since it may drastically influence the diffusion of matter, and thus the microstructural evolution during the elaboration and ageing phases of the materials. The present work concerns NiAl₃ of cementite-type D0₁₁ structure, with a preliminary investigation of its low-temperature point defect structure, based on an independent-point defect approximation. The calculation of the T = 0 K grand canonical (GC) energies E⁰_GC(d) of the point defects shows the mixed antisite-vacancy character of this compound at low temperature. The defect-induced phonon properties are then tackled by means of a harmonic analysis around the T = 0 K relaxed configuration of each type of point defect: although point defects entail only minor changes in the overall shape of the phonon density of states with respect to that pertaining to the undefected reference crystal, they significantly modify the defect parameters, the relevant quantities becoming the (phonon-corrected) GC free energies F_GC(d) = E⁰_GC(d) + F^vib_GC(d), with F^vib_GC= E^vib_GC -TS^vib_GC. Our analysis demonstrates that, in the latter expression, none of the energy and entropy terms can be neglected in general. Moreover, the F^vib_GC term being a decreasing (resp. increasing) function of T for antisites (resp. vacancies), phonon-induced inversions of defect populations are expected at moderate temperatures.

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