Thermodynamics of the congruent vaporization of nonstoichiometric refractory compounds

A study is made of thermodynamic conditions for the congruent vaporization of nonstoichiometric refractory compounds $\mathrm{MX}_y$ in a vacuum. It is shown thatthe character of vaporization at the given temperature is determined by the dependence of free energy on the composition of the compound. A functional relationship is established between the composition of the congruently vaporizing nonstoichiometric compound and the vaporization temperature. Features of the hightemperature vacuum evaporation of niobium carbide are discussed.