Thermodynamics and nonstoichiometry in the D03 compound Ni3Sb

The thermodynamic activity of antimony was determined for nickel–antimony alloys in the composition range between 20 and 52 at% Sb by means of a Knudsen Effusion Mass Spectrometric (KEMS) method. The experimental data in the homogeneity range of the hexagonal γ-NiSb phase (B8-type) were compared with the literature data obtained by a different method. For the activity values in the nonstoichiometric compound Ni₃Sb (D0₃-type), a statistical-thermodynamic model was applied which uses the energies of formation of the six different types of point defects, obtained from ab initio calculations, as parameters. According to these formation energies, the most prominent point defects in nonstoichiometric Ni₃Sb are nickel vacancies. It was found that the inclusion of a full volume relaxation in the ab initio calculations improves the fit of the theoretical curve considerably.