Phase relations and thermodynamics of nonstoichiometric vanadium sulfide in the range VS through V 3S 4

The composition-equilibrium sulfur pressure relation at 750 through 1217°C in the range VS through V ₃S ₄ was determined by using an H ₂H ₂S technique. At temperatures above 888°C a horizontal part in the P_{S 2}-composition isothermal line was observed, which indicated the existence of a two-phase region. At low temperatures, however, it was not recognized. A statistical thermodynamical treatment which started with the V ₃S ₄-type model was attempted by considering three kinds of interaction energies. Qualitative trends of the experimental results at the temperatures above 888°C were interpreted on the basis of the discussed model.