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 degrees C through the Bi2S3 -> BiS2 + Bi + S reaction with the formation of BiS2-I (a = (15.74 +/- 0.01) angstrom, b = (4.026 +/- 0.004) angstrom, c = (11.34 +/- 0.01) angstrom, beta = 127.51 degrees, D-x = 6.36 g/cm(3), V/Z = 71.31 angstrom(3)), and a new metastable high-pressure phase BiS2-II with mmm symmetry (a = (8.45 +/- 0.01) angstrom, b = (10.26 +/- 0.01) angstrom, c = (5.87 +/- 0.007) angstrom, D-x = 7.12 g/cm(3), V/Z = 63.695 angstrom(3), Delta V/V-0 = 0.11) appears at p = 8-8.5 GPa and T >= 1100-1300 degrees 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.