Thermodynamics of the solid Ni-S system

Published measurements of sulfur vapor pressure were used to determine thermodynamic properties of the solid Ni-S system above 800 K. They were Gibbs-Duhem integrated to estimate the formation properties of stoichiometric Ni₃S₂, NiS, and NiS₂. Statistical thermodynamics was applied to find partition functions, interaction energies, and free energies to find possible atom arrangements in Ni_3±x S₂ and Ni_1−x S. Theoretical calculations indicated that nickel vacancies may exist in quasichemical order in the former phase and randomly in the latter phase. A strong indication was that Ni_3±x S₂ should have a sulfur bcc structure with nickel atoms distributed in octahedral sites having a Ni₅S₄ configuration. The possible existence of sulfur vacancies was theoretically investigated.