Investigation of the interaction and composition of vapor in Bi: X(S, Se, Te): Br = 1: 1: 1 systems

The vapor pressure in Bi: X (S, Se, Te): Br = 1: 1: 1 systems was measured by the static method using a membrane null manometer in the temperature range 300–1220 K and pressures 1–900 mm Hg. In the Bi-S-Br and Bi-Se-Br systems, the chemical interaction between the components begins at room temperature, and in the Bi-Te-Br system at 170 C. However, the formation of BiXBr ternary compounds going on only in the range of 350–400 C as a result of the interaction bismuth with chalcogen bromides according to the scheme X2Br2 (l) + 2Bi(s) → 2BiXBr (s). When heated above 400 C in the Bi-Te-Br system, above 420 and 460 C in the Bi-S-Br and Bi-Se-Br systems, the dissociation of ternary compounds going on according to the scheme 3BiXBr (l) → BiBr3 (vapor) + Bi2X3 (s). Based on the temperature dependences of the equilibrium constant of the reaction, the enthalpies and entropies of dissociation reactions are determined. The composition of the vapor after dissociation processes was defined.