New pressure-induced phase transitions in bismuthinite

The study of the effect of high pressure and high temperature on the crystal structure of Bi2S3 has revealed that Bi2S3 decays chemically at p = 6–8 GPa and T = 625–1050°C through the Bi2S3 → BiS2 + Bi + S reaction with the formation of BiS2-I (a = (15.74 ± 0.01) Å, b = (4.026 ± 0.004) Å, c = (11.34 ± 0.01) Å, $\beta = 127.51^\circ $ , Dx = 6.36 g/cm3, V/Z = 71.31 Å3), and a new metastable high-pressure phase BiS2-II with mmm symmetry (a = (8.45 ± 0.01) Å, b = (10.26 ± 0.01) Å, c = (5.87 ± 0.007) Å, Dx = 7.12 g/cm3, V/Z = 63.695 Å3, ΔV/V0 = 0.11) appears at p = 8–8.5 GPa and T ≥ 1100–1300°C. The BiS2-II phase in mixture with the BiS2-I phase is also formed in the Bi + S(1 : 2) composition at the same pressures and temperatures. Chalcogenides of the V2VI3 composition (V = As, Sb, Bi; VI = S, Se) demonstrate a pronounced tendency to thermal instability with the formation of chalcogenides with “incorrect” VVI2 stoichiometry such as AsS2, AsSe2, BiS2-I, BiS2-II, and BiSe2, but the layered structures of these metastable high-pressure phases are different. It can be assumed that the pressure-induced V2VI3 → VVI2 + VVI and V2VI3 → VVI2 + V + VI decay reactions into compounds with incorrect stoichiometry are a general property of these chalcogenides.