Phase equilibria in the Tl₂S–PbS–GeS₂ system and crystal structure of Tl_0.5Pb_1.75GeS₄

Chem. Met. Alloys 5 (2012) 37-41

https://doi.org/10.30970/cma5.0205

M.Yu. MOZOLYUK, L.V. PISKACH, A.O. FEDORCHUK, I.D. OLEKSEYUK, O.V. PARASYUK

The phase equilibria in the quasi-ternary system Tl₂S–PbS–GeS₂ at 520 K were investigated by XRD methods. Three intermediate quaternary phases were discovered, Tl₂PbGeS₄, ~Tl₂PbGe₃S₈ and Tl_0.5Pb_1.75GeS₄. The crystal structure of the quaternary phase Tl_0.5Pb_1.75GeS₄ was determined by powder XRD in the non-centrosymmetric space group I-43d, Z = 16 and a = 1.420082(6) nm (Ag_0.5Pb_1.75GeS₄ structure type). Atomic parameters were refined in the isotropic approximation (R_I = 0.0496, R_p = 0.0944). The phase diagram of the Tl₂GeS₃–PbS section was investigated. The section is quasi-binary, of the eutectic type, with formation of the equimolar compound Tl₂PbGeS₄, which melts incongruently at 781 K and undergoes a polymorphous transformation at 688 K. The НТ-modification crystallizes with a monoclinic structure (S.G. P12/a1, а = 0.89079(7), b = 0.90951(7), c = 1.04772(7) nm, β = 94.116(7)°).

Fragment of the Tl_0.5Pb_1.75GeS₄ structure where Ge-centered tetrahedron is surrounded by the atoms of metallic components, and mutual positions of the thermal ellipsoids of atoms

Keywords

Thallium chalcogenides / Crystal structure / Phase diagram / Isothermal section